What are some medium-level games that I could design an AI for?

This is related to an earlier question about active contests. Since I have not yet found an active contest, I may just end up designing an AI just to design an AI. It will probably be good practice.

But before I go designing an AI, I have to choose what to make an AI for. There are many games such as chess, checkers, go, etc. that are too complicated for me, and have had tons of AI’s written for them in the past. The games tic-tac-toe and RPS are really easy.

I am looking for something where there is no known perfect strategy, but is relatively easy to be relatively okay at, but there is some advanced strategy. I want there to be at least some notion of offense vs defense.