As far as I was able to implement tic-tac-toe for an interview that was time boxed. Although they don't send you a list of every feature that you develop if you can move extremely fast, at least the following features are still missing:

1. Properly detect end game conditions of WIN / LOSE / TIE
2. Actually implement a functional computer opponet (unbeatable? minimax?). Initially it just makes a valid move, not a good one.

Since I was writing this as fast as possible in order to try to get as far into the problem, the following were the things I expected to change from my initial implementation over time:

1. Players are basically just glorified string representing the letter they chose. This is where I'd want board introspection, and would have the computer logic live.
2. The board needs to be readable by the Player, so in addition to the stringer, it would need to return a [3][3]string representation for analyzing.

Beyond that, I wasn't sure where they were going to have me run with it, but here you are.