Free Portal downloaded 1.5 million times

Offer ends May 24.

Valve's revealed that its ongoing promotion which has seen Portal made available as a free download has, rather unsurprisingly, been very successful.

Approximately 1.5 million downloads of Portal have been made so far and the offer is good until May 24. There's no indication of how the downloads have been split between PC and Mac.

The roll-out of new titles for Steam on Mac also continues with a dozen new games:

Madballs in Babo: Invasion
Killing Floor
Altitude
Europa Universalis 3
Hearts of Iron 3
Sam & Max Season 2
Sam & Max Season 3 - Ep. 2
Chains
Simplz Zoo
Caster
Eschalon Book 1
Windosill

Each of these games supports Steam Play, meaning one purchase will work on both Windows and Mac from any computer.