Heya, I’ve got the GRiSP the other week and got around to giving it a spin today, but the USB serial console doesn’t show up in either Windows or OSX.
The rainbow blinky works so I guess that it’s booting but neither in /dev/tty* in OSX nor in the device manager in windows I can find a corresponding USB serial port.
Do I have to install some drivers or something?
Hi! 
It could be that the cable is incompatible. And sometimes it can be necessary to install extra FTDI drivers (depending on OS versions among other things). We have an FAQ entry about this: Frequently Asked Questions · grisp/grisp Wiki · GitHub
Can you try the tips there to see if it helps?
Ohh good call on the cable, I never thought of that being a thing, 3rd one is a charm 
all working now thank you!