While the SDK is open source (in the sense that you can read the source code), Microsoft isn't actively accepting significant contributions according to their Contributing.md, which is somewhat disappointing.

Any bots you build on Microsoft's framework as far as I can tell are also locked into a closed Microsoft-controlled system. Just because it's readable on Github and pushes messages to Slack doesn't really mean that it's open-source in the way we've come to expect from Linux, etc.

I'm building a free-as-in-speech alternative.