Some iPad games don’t have a separate co-op mode, but the single-player mode is still fun to play cooperatively with a friend due to the multi-touch capabilities of the iPad display. These games include Twin It!, Puzzlejuice, Chocobo Panic, and now Hundreds, #3 on the iPad Paid Apps list on the App Store right now.

The goal of Hundreds: Grow at least 100 points between the circles in each puzzle. Circles turn red and volatile while being grown and if they collide, it’s game over. As the levels advance in difficulty, often two people working on the puzzle at the same time can help get to 100.

“My wife was looking on as I was playing and joined in for some co-op multi-touch fun, it was a blast.” -Ron Carmel – Co-creator of World of Goo

Hundreds is 40% off until January 10, 2013.