Any Open-Source RCS apps yet?

Are there any apps that support RCS that aren't made by Google or a crappy cellular provider (ie: bloatware Verizon apps)?

I appreciate the features RCS has, but I'd love to get that without sending it all to Google with a "trust us" approach to backdoor keys. The documentation I looked at indicated that anyone could setup an app to support RCS and communicate with Google's RCS users, but I can't find any apps that actually do that.

Also would love to be able to message from multiple devices using RCS, which Google has working in their web app.