Atomino

Atomino is a 1990 puzzle video game originally for the Amiga, Atari ST and MS-DOS. A version was made for the Commodore 64 in 1991. The objective is to build molecules from atoms, with gradually increasing difficulty and speed.

Rules
The player is given a grid on which to place atoms, which are supplied at random into a stack. An atom needs a specific number of "bonds", from 1 to 4, which are made by placing atoms next to each other. When all connected atoms have exactly the correct number of bonds, a molecule is completed, and it is removed from the board.

Atoms can be placed on a space, or swapped with an existing atom, which will enter the stack. For instance, even if you place an atom needing 4 bonds on the edge, where it has only 3 neighbors, it can be overwritten with an atom needing fewer bonds.

At each level, an objective is given, like "Build 2 molecules" or "Build 4 molecules with at least 9 atoms". In addition to completing the objective, the player must remove all atoms from the board before the next level starts.