I'm new to the OSTC platform but have a thorough SW development background. I've been trying to find info on the "software development kit" for OSTC, but have so far failed to get a complete picture. I managed to find a couple of threads in german, but they didn't quite do the trick. Probably because my german isn't what it should be...

Could someone please summarize (in english) what is needed in order to start programming in terms of IDE etc? I'd like to know as much as possible about compilers, debugging possibilities, available(?) simulators/emulators etc.
My main target platform is Mk2, but feel free to add information on specific differences (from a SW development point-of-view) between Mk1, Mk2 and DR5.
No need to reinvent the wheel by re-writing what has already been written (if already available), but I need some pointers and/or URLs. If possible I'd like to stick to Mac but I have no problems with other platforms as well if needed (or perhaps even preferred for some reason)
Best regards
/Jonas