Gamasutra reports that in the weeks preceding its launch on the shiny new Steam for Mac client, Runic Games' top-down RPG Torchlight hit a pretty substantial milestone. Since its launch last October the game, which typically sells for $20, has been purchased over 500,000 times.

We imagine Perfect World, the game's publishing partner that recently purchased a majority stake in Runic, is pleased as punch about reaching the sales milestone. You should be, too -- in honor of hitting the half-million mark, and in celebration of the game's launch on Mac, you can grab Torchlight on Steam for $10 for a limited time.