Update watchlist: add Ecko fork

watchlist-for-activitypub-apps.md

@@ -24,6 +24,8 @@
 
 * :tada: :heavy_check_mark: **[Dolphin](https://github.com/syuilo/dolphin)**: Lightweight ActivityPub Server optimized for single-user. A fork and sister project of Misskey `AGPL-3.0, Javascript`
 
+* :tada: :heavy_check_mark: **[Ecko](https://github.com/magicstone-dev/ecko)** ([Fedi account](https://c4.social/@weex)): A fork of Mastodon to optimize toward community, that is making it as easy as possible to contribute `AGPL-3.0, Ruby`
+
 * :tada: :heavy_check_mark: **[Epicyon](https://gitlab.com/bashrc2/epicyon)** ([site](https://epicyon.net)): ActivityPub server implementing S2S and C2S protocols, suitable for single board computers. Includes features such as moderation tools, post expiry, content warnings, and image descriptions `AGPL-3.0, Python`
 
 * :heavy_check_mark: **[FlockingBird](https://github.com/flockingbird/roost)** ([site](https://flockingbird.social), [Fedi account](https://fosstodon.org/@flockingbird): social network for professionals (WIP)