Hi!
I'm one of the Renoise devs (see
www.renoise.com). We stumbled upon a problem with Reaper on OSX, which might interest you as well:
When MIDI clock syncing Reaper with Renoise (Reaper as master, Renoise as Slave) via the IAC-Bus, Renoise will not properly sync to Reaper. This happens because Renoise currently relies on the MIDI packet timestamps as primarily timing info, but Reaper seems to ignore the MIDI packet timestamps (sets them to zero).
We've added a workaround for this in Renoise now, but you might want to fix this in Reaper as well. This could cause problems in other MIDI apps as well.
If you do not schedule MIDI events (always send them in realtime), simply setting the packet times to ::AudioGetCurrentHostTime() should do the trick...