Lately I've been thinking (too much) about fusing hexagonal chess with a hexcrawl, and here's what I came up with. It requires an RPG ruleset but it's system-agnostic. I imagine something like Traveller but you could probably do it with a fantasy setting or anything else. It's an OSR-feeling kinda thing. The important part (I think) is that the RPG system should have very simple, cut-and-dry, combat rules.
Disclaimer: This is a first pass. I don't expect it to be 100% playable yet, as I'm sure there are missing bits and unconsidered edge cases. But I think it's done enough to start playtesting, so here I go!
Two groups are warring for control of an alien planet. Neither is very familiar with the local lifeforms. Write statblocks for each piece using your chosen RPG system.
- When you move a piece into or through a hex no one has occupied before, roll its terrain and climate (perhaps using the Welsh Piper rules), and draw the terrain icon on the board.
- Every time a piece ends its move, make an encounter roll based on terrain and climate.
- If an encounter occurs, that unit must defeat or bypass the encounter before proceeding.
- If an encounter occurs in a hex occupied by two opposing pieces (i.e., a capture has just been attempted), roll 1d6 to determine which side is affected by the encounter: (1-2) attacker, (3-4) defender, (5-6) both. If both sides are involved in the encounter, it's up to the players to determine whether or not they cooperate; think Braunstein-level roleplay.
- When a unit defeats an encounter, roll 1d6 for the value of the Treasure found there. If both sides shared in the victory, each side gets 1d3.
- Treasure Points accumulate and may be used to purchase new pieces (using traditional chess scoring rules: pawn=1, bishop or knight=3, rook=5).
- New pieces must be purchased at the beginning of one's turn, and must enter the board via one of the original starting positions for that piece.
Piece moves are based on:
Dragonfly Chess by Christian Freeling
...which is based on Gliński's Hexagonal Chess by Władysław Gliński
Here's a demo video showing 15 turns of Hexcrawl Chess, using D&D and the Wilderness Hexploration rules:
For extra flava, consider adding a GM.