I just replaced an EventMachine-based project with Celluloid::IO - it was a pretty simple replacement, although I had some issues with concurrent connections (https://github.com/celluloid/reel/issues/11).

I have yet to test it in production, but it looks pretty promising.

I had a lot of problems with EM blocking networks connections if an event loop was tying up CPU, but I suppose that's to be expected.