I've been part of quite a few game jams over the years. Ludum Dare about twice a year, a few jams at school and other game jams me and my friends have stumbled upon.
I also have a few games that aren't game jams, but small scale enough that they essentially are.
Estimated Time of Arrival was a game me and a group of 7 people for Ludum Dare 43 over a 3 day period.
The theme for the jam was "Sacrifices must be made", so we designed a game around the idea that you had to sacrifice your own character, and then respawn at the start of the level to make progress. The twist being that your previous self also played the level along side you.
Seedling was a game me and a group of 6 people for Ludum Dare 45 over a 3 day period.
The theme of the jam was "Start with Nothing", so our idea was to create a 2D-platformer where there was no level initially. We went about this by creating a system where the player could grow trees by planting seeds and then watering the tree to have some control over where it grew.
Subrawl was not technically a game jam, but a small scale student project at Future Games. With a group of 6 people we made a small game in one week inspired by retro game mechanics and pixelated graphics.
Fire Keeper was a game me and a group of friends made for Ludum Dare 46 over a 3 day period.
The theme of the jam was "Keep it alive", our idea was based on two things, firstly to have the player keep a flame alive through the level, by protecting it from wind and water. Secondly by promoting the player to speedrun through the level as fast as they can, keeping their momentum alive or "keeping their run alive"