Alright, the basic idea is really simple:
1. Give everyone 3 cards; color 'em differently for each player, and make sure you can tell the difference between the front and back.
2. Place the cards in front of you face up.
3. Whenever you take an action, flip that action's cost in cards face down.
4. You don't have to have spend all your cards in a turn; after you take all the actions you want, pick someone who still has face-up cards in front of them to go next.
5. The round ends when all cards are face down.
6. When a round starts, flip all cards face up.
OK, sounds kinda alright... it doesn't take advantage of the fact that we're using physical props to keep track of our actions. So we'll add a special action.
7. A player may gift a card to another player. This is an action that costs one card; pick one of your face-up cards and put it in front of another player face-up.
8. Whenever you would flip a card of another player's color face up, put it in front of them face down instead.
I feel this would do for an example: Assume for now that attacks cost 2 cards and movement costs 1.
Alice and Bob get in a fight with the nefarious Eve, who ambushes them out of nowhere (and therefore goes first).
Eve flips one card to move to where Bob is, and flips two cards to strike him with her horrific Neutronium Mace. She then passes her turn to Alice, who is two moves away, and therefore wouldn't be able to reach her to make an attack.
Bad move on Eve's part; Alice flips one card to move towards Eve, and then flips another to put her last card in front of Bob, passing the action to him.
Bob now has four cards in front of him; one red, three blue. He flips all of them to make two attacks against Eve, stabbing her viciously with his +8 Sword of Stabbitude. All cards are flipped, so the round ends.
Everyone flips their cards face up; however, Alice is still down a card because the card she gave Bob didn't flip back face-up. After all, he only gave it back to her.
Now the fight progresses as normal, but with Alice 1 card down.
Now, there are some interesting things you can do with the "action gift" mechanic; for example, you could make a Rogue class who gets a sizable bonus if one of the cards used in an attack isn't theirs.