Forum Spark is my personal favorite free forum host. Cedric took over the service and he's been adding a bunch of awesome features lately! I know Gizmo has a forum host on the service, I do too but it's not ready to be promoted yet. I highly recommend checking out FS if you're looking for a free forum host, you won't be disappointed! https://forumspark.net/
It is awesome. It's definitely Revillution's backup if our hosting does go to shit and we can't find a suitable replacement. Super easy to convert from XF to FS too!
Super easy to convert from XF to FS too!