They did it last year, and they still haven't finished their game so they're doing it again this year. Desktop Dungeons was/is a brilliant little mash-up of rogue-like and puzzle game, and the devs have been working on a dramatically expanded version with a metagame, character persistence and all sorts. In honour of GDC, because, er, I don't know, they've made the beta version of the game free to all for the duration of the conference.
You do need to register, you've only got until March 31st and. Well, I don't have an and. Just go play it, I guess. I'm sure it's come on leaps and bounds since last year, and I do keep meaning to check in and see what's new.
If you like what you try, pre-ordering the game now for $10 (or $20 for assorted bells and whistles) gets you ongoing access to the beta. Also, the original version remains free, and a little wonder.
The game's site seems a little unhappy right now, so exercise patience if you can.
I wonder how many words of this post are accidentally identical to the one I wrote last year. I daren't look, for fear of the dark truths it might reveal about my command of English and imagination.