It's not free.
But if you've used it, can you tell me if only one player needs a copy or does everyone need to purchase it?
Every client needs his own copy of the app, though with thousands of free tabletops in the steam workshop library it is kind of a steal. And there is the 4-pack which comes with a decent discount. Besides TTS is a one-time payment, no subscriptions or other strings attached and X-Wing for TTS is awesome as well. And yes, you can combine both games on one table, virtual or otherwise.