I've had the privilege of getting to spend some time up in the mountains this summer (haven't really the last two summers). Being up in the cool, clean air and the quiet always gives me tons of ideas. Here are a few:
Class-based Maps for a Space Game
I've been interested in some non-D&D one-offs, or mini campaigns. One that I think would be fun would be a space ship crew investigating a derelict ship. In trying to figure out how to catch some of that genre flavor, I thought giving each player different maps of the ship being explored would work. The idea is the ship itself is a familiar entity, a federation ship, or one from their own corporation, but their individual knowledge of the ship is limited to their field of expertise. So the engineer knows where the maintenance access ducts are, the medic/science officer knows where life support air ducts are, ect. Then let loose some alien threat and only allow players to share their maps by verbally describing them to each other: "If we get to bulkhead B, there is an air duct there." "Yes there is a maintenance duct access near there too, I think we should head there."
A magic item that you rub on and suffer great burning pain (1d6 hit points lost permanently) but allows you to come back after death-by-fire a whole level higher.
A rare beetle mages catch, whisper a spell to, and then send to a friend in need. The beetle travels at normal speed to where the friend is, and if eaten, grants that friend the ability to cast that spell once. Until they do, that spell slot is lost to the beetle-sending mage, though.
I've long been a proponent for using common parlor games in my D&D-- Jenga, cards, charades - both because if it is that common it is probably good at being amusing but also it is probably something players will have knowledge of, so reduces the amount I have to teach them. I don't think I've written about Yahtzee in this regard. I think it would be perfect for a gambling type situation where you can take small gains that you know, or risk them to push for bigger gains-- two situations that spring to mind are spell research and social maneuvering. Maybe getting to know the local politicians could be that player throwing Yahtzee dice and the higher the hand they end up with the better the relationship established. Or, I was just talking about wanting some type of shopping mini-game, maybe this mechanic could work for that.