Spiderweb Software is celebrating its 20th anniversary by partnering with Humble Bundle to bring Mac gamers thirteen of its full-length role playing games. Like other Humble Bundle deals, you pay what you think it's worth - but anyone who pays more than the average gets two additional games as a thank you. A cut of the proceeds also go to charities: the Electronic Frontier Foundation and Child's Play.

This week's Humble Weekly Sale brings you "every one of [Spiderweb's] games that still runs on a modern Macintosh," according to Spiderweb founder Jeff Vogel. The game includes seven titles in the Avernum Saga, five games in the Geneforge Saga and Avadon: The Black Fortress. If you pay more than the average you also get Avernum: Escape from the Pit and Nethergate: Resurrection. All games are full-length and unencumbered in any way. They're also DRM-free.

Spiderweb specializes in producing turn-based computer role playing games (CRPGs) in the classic style, harkening back to games like Wizardry and Ultima. You control a party of characters from an overhead perspective (depending on the game, Spiderweb uses either a flat 2D view or an isometric/three-quarters view). The games feature deep, branching story lines with many side-quests and adventures to go on, tons of loot to plunder, monsters to kill and stuff to do.

You'll spend hours, if not weeks, playing each one - so thirteen of Spiderweb's games are bound to make you write off most of the rest of the summer. Spiderweb themselves estimate the total play time to be somewhere in the vicinity of 400 hours - that means you can play them for twelve hours a day for a month straight and still not be finished.

This deal only lasts a week, so don't sit on it.

Spiderweb develops RPGs for OS X, Windows and iOS.