Paint War — free browser game

The board is a hexagonal grid of six-coloured cells, generated so no two neighbouring cells share a colour — each hex touches up to six others. You start as the single cell in the bottom-left corner; the AI starts in the top-right. On your turn pick a colour from the palette: every cell you own turns that colour, then your region floods — absorbing all adjacent neutral cells of that colour, chaining outward. The key rule: you may not pick your own current colour nor the opponent's current colour, so each turn you choose one of the remaining four (forbidden colours are dimmed in the palette). Keys 1-6 are colour shortcuts; R restarts. The game ends when no neutral cells remain and whoever owns more cells wins. Tip: grabbing the colour that claims the most cells (greedy play) is good early, but to stop the AI from sealing off a big region you sometimes pick a lower-gain colour to cut off its path.