eventpanda is an API compatible drop-in replacement for EventMachine using FFI and libevent2 instead of the C++ reactor.
Still in beta, but it works. please report any issues :)
Thin / Rack
# runs a rack-app on thin using eventpanda instead of eventmachine as its backend. cd eventpanda ruby -Ilib -reventpanda/em/eventmachine -rrack -e "app = Rack::Directory.new('.'); Rack::Handler::Thin.run(app)"
git clone https://github.com/lian/eventpanda.git
No compilation is required. You must have libevent >= 2.0 installed.
License can be found in the file COPYING.