I didn't know what Warped used (I only listened to the podcasts)
The problem with Fantasy Grounds is that it costs 36€ and then another 20€ for the WOIN DLC.
It's not the actual gameplay that is the trouble, because you can still have a great game over skype of discord chat with no grids or pictures and only using The Theatre of the Mind, but the main issue I mean to address is that of finding players and Roll20 is great for that with other systems, but WOIN being smaller its tougher.