I've tagged the 1.0.0 version of #brutaldon, a brutalist, server-side client for Mastodon and Pleroma. The version number is intended to indicate that all of the basic client functionality is complete. There are a lot of nice-to-haves that can be done on the master branch, and there's a settings/themes branch underway, but the core is all there now.
https://github.com/jfmcbrayer/brutaldon/releases
https://brutaldon.online/