AARP has a ton of great free games to play online, including classics like Solitaire, Daily Crossword, and Sudoku. But I personally like Mahjongg Dimensions. It takes the traditional tile-matching game of Mahjong and turns it into a 3D puzzle. Instead of a flat board, your tiles are stacked into a large cube. You have to spin the block around to find matching pairs on different sides and clear them before the timer runs out.