Sprawlopolis
For me this is the best solo board game. Not only there is a big replayability desire but also it takes very small amount of space on your desk. It’s also very fast to prepare the game for playing it. I can play Strawlopolis anywhere and anytime. I can always find some time to play it because it only contains 18 cards. Of course you need kind of use your brain but one round lasts a couple of minutes! It is also worth saying that fun never ends after one game!