We've done some internally at Endigit. It's always a good time. We have a couple of our favorite challenges up here:
https://endigit.com/wordbattle
and here:
https://endigit.com/squarebattle
But we also do some shorter duration hacks, things that can be done in 20 minutes or so. It could be fun to have a session after the next WaFL User Group meeting.