For those of you who, like me, might want to use this on older hardware, I got an error on launch on Mac OS X 10.8.5 Mountain Lion: https://github.com/CamHenlin/imessageclient/issues/2

Just thought I'd mention it here in case others are thinking of trying this out on Mountain Lion.

Edit: CamHenlin has already committed a fix for this problem. Nice work!