For details on how to build emesene for yourself, see here.
emesene can only run on 64bit systems. Snow Leopard, Lion and Mountain Lion are offically supported. Please note there are still minor quirks with PyGTK on Lion and Mountain Lion. You may have to change your GateKeeper setting on Mountain Lion to allow emesene to launch. Leopard and Tiger are not supported.
Before posting an issue on emesene tracker please do the following:
To find older versions of emesene OS X, see here.