Anyone looking for quality entertainment software for their computers should take advantage of these two limited-time offers.

The first is the Humble Indie Bundle, which packages together six games: World of Goo, Aquaria, Gish, Lugaru, Penumbra, and Samorost 2. All six games are available for PC, Mac, and Linux, making for 18 unique downloads. Customers can name their own price and even determine the proportions by which it is divided among three recipients: the bundle's six developers; Child's Play, a charity that supplies children's hospitals with games; or the Electronic Frontier Foundation. Child's Play is a favorite charity of mine, so the opportunity to benefit them and receive something in return is a win-win.

Of the six games, World of Goo alone is worth the price of admission. In October 2009, its developer, 2D Boy, conducted a experiment similar to this bundle in which gamers could pay whatever they wanted for Goo. The results are extensively documented and, like the current Humble Indie Bundle findings, reflect that those who use a free operating system tend to be the most generous with their monies.

If donating to charity for a half-dozen games isn't your thing, then how about just one title for free? Portal, Valve's first-person puzzler that has won multiple awards, is a free download through the Steam service through May 24th. It's part of a promotion of Steam's availability for the Mac, launched this week. Any Mac games you previously bought for PC can be downloaded for free, but whether or not you're an existing customer, you can now get Portal for either platform by signing up for a free Steam account.

Portal is a groundbreaking game in its own right, and with Portal 2 coming out later this year, now is a good time to catch up on what you've missed.