tangled.org
matrixfurry.com
A built-in package registry would be super useful to have. I maintain a Homebrew tap, and plan to maintain OS images in the future, both of which require a package registry to work well. Right now, I'm using GitLab for that.
Examples from other forges:
(I'm really tired right now so I'll probably update this tomorrow with more info)
jcg.re
indexx.dev
I'd really like an atproto package registry, but I don't think bundling that into tangled is the right call. It feels like this could/should be a separate project.