It's all in browser, supports up to 6 player multiplayer card games, BYO cards (user uploads card images). YES you can spectate games if you want to have a look.
This has been a growing industry, i have noticed in the last 4 years people like the idea of being in control of their game, playing on the mistakes their opponents make and having the skill to think about the game with out the computer doing the work for you like in most digital card/boardgames from today.
Untap.in is a personal project, has about 100k registered users and 1600 daily active, its a big community. All of this is being serviced by a sole dev (myself) in my free time. The likes of these frameworks should make it extremely easy to get board games through prototype and playable, its a great thing.