* [frp](https://github.com/fatedier/frp) [![frp github stars badge](https://img.shields.io/github/stars/fatedier/frp?style=flat)](https://github.com/fatedier/frp/stargazers) - Comprehensive open alternative to ngrok. Supports UDP, and has a P2P mode. I believe it uses a custom TCP protocol for multiplexing, which can either run over a single TCP connection or a connection pool.
* [ngrok 1.0](https://github.com/inconshreveable/ngrok) [![ngrok 1.0 github stars badge](https://img.shields.io/github/stars/inconshreveable/ngrok?style=flat)](https://github.com/inconshreveable/ngrok/stargazers) - Original version of ngrok. No longer developed in favor of the commercial 2.0 version.
* [localtunnel](https://github.com/localtunnel) [![localtunnel github stars badge](https://img.shields.io/github/stars/localtunnel/localtunnel?style=flat)](https://github.com/localtunnel/localtunnel/stargazers) - Written in node. Popular suggestion.
* [kcptun](https://github.com/xtaci/kcptun)[![kcptun github stars badge](https://img.shields.io/github/stars/xtaci/kcptun?style=flat)](https://github.com/xtaci/kcptun/stargazers) - A Stable & Secure Tunnel based on KCP with N:M multiplexing and FEC. Available for ARM, MIPS, 386 and AMD64. Written in Go.
* [Teleport](https://goteleport.com/) [![teleport github stars badge](https://img.shields.io/github/stars/gravitational/teleport?style=flat)](https://github.com/gravitational/teleport) - Comprehesive control plane tool, but also supports [accessing apps](https://goteleport.com/docs/application-access/introduction/) behind NATs. Written in Go.
* [Nebula](https://github.com/slackhq/nebula) - [![nebula github stars badge](https://img.shields.io/github/stars/slackhq/nebula?style=flat)](https://github.com/zerotier/slackhq/nebula) Peer-to-peer overlay network. Developed and used internally by Slack. Similar to Tailscale but completely open source. Doesn't use WireGuard. Written in Go.
* [ZeroTier](https://www.zerotier.com/) - [![zerotier github stars badge](https://img.shields.io/github/stars/zerotier/ZeroTierOne?style=flat)](https://github.com/zerotier/ZeroTierOne/stargazers) Layer 2 overlay network. They take decentralization seriously, and like to say "decentralize until it hurts, then centralize until it works." Written in C++.
* [sshuttle](https://github.com/sshuttle/sshuttle) [![sshuttle github stars badge](https://img.shields.io/github/stars/sshuttle/sshuttle?style=flat)](https://github.com/sshuttle/sshuttle/stargazers) - Open source project originally from one of the founders of Tailscale. Server doesn't require root; client does. Explicitly designed to avoid TCP-over-TCP issues.
* [chisel](https://github.com/jpillora/chisel) [![chisel github stars badge](https://img.shields.io/github/stars/jpillora/chisel?style=flat)](https://github.com/jpillora/chisel/stargazers) - SSH under the hood, but still uses a custom client binary. Supports auto certs from LetsEncrypt. Written in Go.
* [expose](https://github.com/beyondcode/expose) [![expose github stars badge](https://img.shields.io/github/stars/beyondcode/expose?style=flat)](https://github.com/beyondcode/expose/stargazers) - ngrok alternative written in PHP.
* [rathole](https://github.com/rapiz1/rathole) [![rathole github stars badge](https://img.shields.io/github/stars/rapiz1/rathole?style=flat)](https://github.com/rapiz1/rathole/stargazers) - Similar to frp, including the config format, but with improved performance. Low resource consumption. Hot reload. Written in Rust.
* [go-http-tunnel](https://github.com/mmatczuk/go-http-tunnel) [![go-http-tunnel github stars badge](https://img.shields.io/github/stars/mmatczuk/go-http-tunnel?style=flat)](https://github.com/mmatczuk/go-http-tunnel/stargazers) - Uses a single HTTP/2 connection for muxing. Need to manually generate certs for server and clients.
* [sish](https://github.com/antoniomika/sish) [![sish github stars badge](https://img.shields.io/github/stars/antoniomika/sish?style=flat)](https://github.com/antoniomika/sish/stargazers) - Open source ngrok/serveo alternative. SSH-based but uses a custom server written in Go. Supports WebSocket tunneling.
* [Tinc](https://github.com/gsliepen/tinc) [![tinc github stars badge](https://img.shields.io/github/stars/gsliepen/tinc?style=flat)](https://github.com/gsliepen/tinc/stargazers) - Tinc is a peer-to-peer VPN daemon that supports VPNs with an arbitrary number of nodes. Instead of configuring tunnels, you give tinc the location and public key of a few nodes in the VPN. After making the initial connections to those nodes, tinc will learn about all other nodes on the VPN, and will make connections automatically. When direct connections are not possible, data will be forwarded by intermediate nodes. Written in C.
* [tunnelto](https://tunnelto.dev/) [![tunnelto github stars badge](https://img.shields.io/github/stars/agrinman/tunnelto?style=flat)](https://github.com/agrinman/tunnelto/stargazers) - Open source (MIT). Written in Rust.
* [wstunnel](https://github.com/erebe/wstunnel) [![wstunnel github stars badge](https://img.shields.io/github/stars/erebe/wstunnel?style=flat)](https://github.com/erebe/wstunnel/stargazers) - Proxies over WebSockets. Focus on proxying from behind networks that block certain protocols. Written in Haskell with executables provided.
* [Crowbar](https://github.com/q3k/crowbar) [![crowbar github stars badge](https://img.shields.io/github/stars/q3k/crowbar?style=flat)](https://github.com/q3k/crowbar/stargazers) - Tunnels TCP connections over HTTP GET and POST requests.
* [boringproxy](https://boringproxy.io/) [![boringproxy github stars badge](https://img.shields.io/github/stars/boringproxy/boringproxy?style=flat)](https://github.com/boringproxy/boringproxy/stargazers) - Designed to be very easy to use. No config files. Clients can be remote-controlled through a simple WebUI and/or REST API on the server.
* [tunneller](https://github.com/skx/tunneller) [![tunneller github stars badge](https://img.shields.io/github/stars/skx/tunneller?style=flat)](https://github.com/skx/tunneller/stargazers) - Open source. Written in Go.
* [jprq](https://github.com/azimjohn/jprq) [![jprq github stars badge](https://img.shields.io/github/stars/azimjohn/jprq?style=flat)](https://github.com/azimjohn/jprq/stargazers) - Proxies over WebSockets. Written in Python.
* [tunnel](https://github.com/koding/tunnel) [![tunnel github stars badge](https://img.shields.io/github/stars/koding/tunnel?style=flat)](https://github.com/koding/tunnel/stargazers) - This one is a Golang library, not a program you can just run. However, it looks easy to use for creating custom solutions. Uses a single TCP socket, and [yamux](https://github.com/hashicorp/yamux) for multiplexing.
* [pgrok](https://www.proxy.jetzt/) [![pgrok github stars badge](https://img.shields.io/github/stars/jerson/pgrok?style=flat)](https://github.com/jerson/pgrok/stargazers) - Fork of ngrok 1.0, with more recent commits.
* [SirTunnel](https://github.com/anderspitman/SirTunnel) [![SirTunnel github stars badge](https://img.shields.io/github/stars/anderspitman/SirTunnel?style=flat)](https://github.com/anderspitman/SirTunnel/stargazers) - Minimal, self-hosted, 0-config alternative to ngrok. Similar to sish but leverages Caddy+OpenSSH rather than custom server code.
* [remotemoe](https://github.com/fasmide/remotemoe) [![remotemoe github stars badge](https://img.shields.io/github/stars/fasmide/remotemoe?style=flat)](https://github.com/fasmide/remotemoe/stargazers) - SSH-based, with custom golang server. Does some cool unique things. Instead of just plain tunnels, it drops you into a basic CLI UI that offers several useful commands interactively, such as adding a custom hostname. Also allows end-to-end encryption for both HTTPS and upstream SSH. Doesn't appear to offer non-e2e HTTPS, ie no auto Let's Encrypt support.
* [StaqLab Tunnel](https://tunnel.staqlab.com/) [![staqlab github stars badge](https://img.shields.io/github/stars/abhishekq61/tunnel-client?style=flat)](https://github.com/abhishekq61/tunnel-client/stargazers) - SSH-based. Client is open source. Server doesn't appear to be.
* [SSH-J.com](https://bitbucket.org/ValdikSS/dropbear-sshj/) - Public SSH Jump & Port Forwarding server. No software, no registration, just an anonymous SSH server for forwarding. Users are encouraged to use it for SSH exposure only, to preserve end-to-end encryption. No public ports, only in-SSH connectivity. Run `ssh ssh-j.com` and it will display usage information.
* [Ngrok-operator](https://github.com/zufardhiyaulhaq/ngrok-operator) - Ngrok but integrated with Kubernetes, allows developers on private kubernetes to easily access their services via Ngrok.
* [ngrok 2.0](https://ngrok.com/) - Probably the gold standard and most popular. Closed source. Lots of features, including TLS and TCP tunnels. Doesn't require root to run client.
* [CloudFlare Tunnel](https://developers.cloudflare.com/cloudflare-one/connections/connect-apps/install-and-setup) - Excellent free option. Nicely integrates tunneling with the rest of Cloudflare's products, which include DNS and auto HTTPS. Client [source code](https://github.com/cloudflare/cloudflared) is Apache 2.0 licensed and written in Golang.
* [Tailscale](https://www.tailscale.com/) [![tailscale github stars badge](https://img.shields.io/github/stars/tailscale/tailscale?style=flat)](https://github.com/tailscale/tailscale/stargazers) - Built on WireGuard. Easy to use. Doesn't include an HTTPS proxy on the public side, but could be combined with nginx/Caddy/etc. Client [code](https://github.com/tailscale) available with a BSD3 license + separate patents file.
* [Loophole](https://loophole.cloud/) - Offers end-to-end TLS encryption with the client automatically getting certs from Let's Encrypt. QR codes for URL sharing. Client is open source. Can serve a local directory over WebDAV. MIT License. Written in Go.
* [Packetriot](https://packetriot.com) - Comprehensive alternative to ngrok. HTTP Inspector, Let's Encrypt integration, doesn't require root and Linux repos for apt, yum and dnf. Enterprise licenses and self-hosted option.
* [Hoppy](https://hoppy.network/) - WireGuard-based. Provides static IPv4 and IPv6 addresses for your machines, which is a simple and useful level of abstraction. Targeted towards self-hosters and people behind NATs.
* [gw.run](https://gw.run/) - Specifically focusing on securely exposing internal web apps to a group of people; not for publicly facing apps. Share access via email address then allow users to log in with common login providers like Google.
* [inlets](https://inlets.dev/) - Used to be [open source](https://github.com/inlets/inlets-archived); now focused on a polished commercial offering. Designed to work well with Kubernetes.