WizenWorld is a free math adventure game for 3rd - 8th graders, aligned to the Common Core. Practice fractions, decimals, arithmetic and much more... for free!
Lure of the Labyrinth is a digital game for middle-school pre-algebra students. It includes a wealth of intriguing math-based puzzles wrapped into an exciting narrative game in which students work to find their lost pet - and save the world from monsters! Linked to both Common Core and national (NCTM) standards, the game gives students a chance to actually think like mathematicians.
Quandary is a free, award-winning game that engages your students in ethical decision-making and develops skills that will help them recognize ethical issues and deal with challenging situations in their own lives.