Pocket Battles series. Plays like Magic (pre-building, etc) only without the CCG aspect
All the pocket battles games are basically the same - so you can mix and match opponents from different packs.
You have a number of troop pieces, advncing and fighting in a fairly abstract left flank / centre / right flank manner. In a combat, each troop card has a number of dice symbols on it (e.g. a card might show a 5 and a 6). You roll a number of dice (normally 1, but this can be varied depending on charges etc. Each dice that comes up with a number showing on the troop card does one hit to the enemy. Most cards can take 1 hit, some can take 2.
The strategic bit is that each turn you will have so many order counters to play with. Ordering a unit more than once in a phase will take geometrically more order tokens.....and, any unit that gets wounded costs you a unit token: the order token is flipped to the wound side and placed on the unit. You've lost it until that unit is wiped out.
Pocket Battles are fun little games to pass 20-30 minutes. Don't expect Romans to play dramatically different from Orcs, or Persians. I wouldn't spend an evening playing game after game, but as a filler it does exactly what it says on the tin - gives you a neat little battle with strategic and tactical decisions that you can play in a short timeframe, and that is easily portable.