Garry's Mod, the sandbox application based on Valve's Source engine, has seen sales top 312,541 since its debut on Steam two years ago.
The game's creator, Garry Newman, commented on his surprise that the USD 10 title proved to be such a hit and added that it has since afforded him the opportunity to learn more about games development and programming.
"The day it went on Steam was a nervous day for me. How well would it sell, would it be buggy as hell, would Valve regret giving me this chance?" he wrote on his blog.