New "collections of Mac titles" will be available on Wednesdays, Valve explained today, with "each designed to highlight specific functionalitites of Steam on the Mac."

Tomorrow's launch lineup is meant to demonstrate "'Steam Play,' which allows customers to purchase a game once and play it on all Steam supported platforms," with games including Valve's puzzle-shooter Portal and Runic's action-RPG Torchlight.

"Steam for the Mac solves so many problems for us as a developer," noted Max Scahefer of Runic. "We look forward to our future games coming out on the Mac as well."