Duelyst [official site] is now in open beta. The turn-based strategy game was successfully Kickstarted last year and has been in closed beta for some time, but now anyone can sign up and play via its site.
From some of the same designers as Diablo, Duelyst aims to mix turn-based tactics in small, single-screen battlefields with the use of collectible cards. Marsh liked it a lot when he played the closed beta for us earlier this year, praising the intelligence of its design and the pace of its short, ten-minute rounds.
If you backed the Kickstarter however, you might be less happy. The game was originally meant to be accessed via a one-time fee, with free-to-play apparently not fitting the team's vision for the game. That changed in February of this year when the game made the switch to free-to-play, saying that they'd "run the numbers, and a one-time purchase model simply doesn't support the level of updates we want to bring to you." I have no problem with the free-to-play model in theory, and can cite many good examples of its application, but it must sting if you backed the project on the grounds that it wouldn't be free-to-play.
On the flipside of that, it means you can now try the game for free. Marsh's write-up also found it, compared to other F2P economies, "one of the less aggressive, with an ample supply of cards for each factions unlocked from the start." Real money is mainly used to buy cosmetic items and any card sold for real money can also be bought with in-game funds earned through play. As ever, any of this could change, of course.
You can download the game's launcher for Windows and Mac here. Here's an old gameplay walkthrough explaining how it works: