I use FG Unity, along with Discord. I'm the GM, so I spent the $150 or whatever for the DM version of FG. Also I've spent a few hundred on books, so there are costs to consider with any VTT you decide to use. If you're wanting to fully utilize a VTT like FG or Roll20 or Foundry, you're going to want to get the books, or you're gonna be spending WAY too much time trying to write your own modules to convert the books you own. But if you're just a player, then you don't have to spend anything, it's all on the DM's account and players can just download the free client.