Humble Bundle offers downloads of the Humble Retro Shooter Bundle for Windows and Mac for whatever you want to pay. If you opt to pay the bare minimum of $1, you'll get Shadow Warrior Classic Redux, Serious Sam HD: The First Encounter, Serious Sam HD: The Second Encounter, and Duke Nukem 3D: Megaton Edition. That's $49 under the lowest price we could find for downloads of these games elsewhere.

If you pay more than the average, currently $6, you'll also get System Shock 2 and Hard Reset: Extended Edition. Your contribution can be donated to charity (Electronic Frontier Foundation or Child's Play), the developers, Humble Bundle Inc. Deal ends September 19 at 2 pm ET. Of note, these games require a Steam account for activation.