Keima Go is played like normal go, with two exceptions:
- you have to place two stones instead of just one on each turn you don't pass
- and both stones have to form a keima.
Since each stone captures on its own, one stone may clear the intersection for the other. Neither of them, however, may commit suicide.
After two passes in a row, the result is determined via area scoring. Since this excludes free removal of "dead" stones, and capturing may turn out impossible, quite some "territory" may end spoiled. Considering this, komi is only 2. Usually a 9x9 board is used.
See also http://www.hannover-go.de/Keima-Go/Keima-Go.html (German).
 Variation: three passes, and passes clear ko bans.
gaius: Another suggestion: komi becomes zero, and black's first move consists of only one stone. This way, the game becomes very even. It's also used in the game of six-in-a-row, in which each player gets two moves, except for black's first move, and that game is considered to be very even.
OneTrueCalculus: I would guess that this is good for black; because the two stones are not placed freely, they are not twice as useful as one stone.
metzgerism?: Would the minor advantage that black receives by not forming a Keima be mitigated if their first move was at tengen, thereby forcing them to not have a choice but rather give white the first effective move? Black would have the material evenness.