WUMPUS is a bit of retrocomputing nostalgia. It is an exact clone, even down to the godawful user interface, of an ancient classic game. This version fixes two minor bugs in an earlier 1992 USENET posting of the source. This package also includes superhack, which is a structurally similar game with a different premise.
XWelltris is a 2.5D Tetris-like game. Imagine that you are looking into a glass from the top. You see four walls and the bottom. Flat 2D figures fall down from the walls one by one. You can move these figures from one wall to another or rotate them. If the figure leaves the wall, then it moves to the bottom while another figure is pushed. You need to form full rows or columns on the bottom. When you form such row it disappears and you receive additional empty space on the bottom and your score increases. Extra points are earned by making more rows disappear at the same time. If you can't place a whole figure on the bottom, then it stays on the wall and you can't place figures on that wall for a while.
Real Mah Jongg is a social game that originated in China thousands of years ago. Four players, named after the four winds, take tiles from a wall in turn. The best tiles are made of ivory and wood; they click pleasantly when you knock them together. Computer Solitaire Mah Jongg (xmahjongg being one of the sillier examples) is nothing like that but it's fun, or it must be, since there are like 300 shareware versions available for Windows. This one is for X11 and it's free.