I think by building it for ourselves, we really built something that everyone could appreciate. Not tying it too much to any one language, and encouraging projects from other languages to get on board went a long way to making it feel language agnostic.

We discontinued the gem builder because it was causing confusion in the gem ecosystem and we were unable to build all gems (e.g. those with C extensions or that needed signing). It was a fine experiment, but it didn't end up being the right thing to do.

Those kinds of build tools make more sense to be developed outside of GitHub and hooked in via the API or webhook system.