It's a multiplayer sandbox (no rules enforcement) that just allows you to play by providing all the different zones the game involves (play area, hand, lib, gy, ex) and letting you free-drag between them. It has features for every mechanic the game involves - tapping, turning face-down, switching card control to another player, etc - and it looks good and is smooth and easy to use.

There's nothing like it. Existing options have various constraints/drawbacks or else are so old-fashioned and clumsy as to be nigh-unusable.

I don't know how people will react when I announce. I don't know how Wizards of the Coast will react. I'm a bit nervous about it. I know it's the best of its class, because I play magic, and I have no idea what other people will make of it. It fits their fair-use policy (product must be free, but can be ad-supported or take patreon-revenue) but even so I'm nervous.