Hi.
I’ve been using trackers for 10+ years. I have a renoise licence and I love it… wonderful program.
When I play live I use two laptops running renoise and I will segue from one track to the next on either machine…
Is there a way I can synchronize these 2 instances of Renoise on these two machine, so I don’t have to babysit the beat matching?
I have never used MIDI before, but it sounds like that’s what will make this work.
Is anyone doing this? What do I need to buy to get this going?
Help! 
yes. you’ll need midi on both your computers.
connect the midi-out from one computer (which will be master) to the midi-in from the other (slave).
now in the slave-pc you’ll have to enable the midi-slave button on upper right corner of renoise (the leftmost one with the tiny clock) and under configs->midi set the “midi clock slave settings” in device to the midi device of the computer
in the master pc just go to configs->midi and select your midi device under “midi clock master settings”->out device.
well, that’s it. 
now hitting play on the master pc will also start the slave. and the slave will also adjust the tempo to the master.
you’re welcome. 
to be honest: i actually haven’t tried it over midi.
i used midi-yoke to sync two apps inside one computer (for recording vocals), but the procedure is the same.
i didn’t run both apps in sync that long so i could get the same tempo change thingie you got over there, but maybe it’s a midioverlan problem? i don’t really know. but i’ll check if i get the same problem via midiyoke.