Triumph & Tragedy by GMT Games is a rare example of an excellent three-player game. Having played it a few times, I thought it could be adjusted to a five-player game and amended the rules to accommodate five players.
T&T uses blocks as units and like Stratego and Columbia Games’ block games. The block faces remain hidden unless attacked or attacking. Card play for diplomacy (‘Government Phase’ in T&T lingo) is usually card by card, but Dan divvied up the Phase into a maximum of three sub phases to make it easier for the PBeM umpire. As long as one player plays a card, the next sub phase occurs, but if nobody plays a card, the Government Phase ends. You get an updated map at the end of each sub phase
Few three-player games are interesting. Usually, two gang up on one and that’s that. Give T&T credit. It’s one of the few three-player games that seems to work.