Video game idea I'd like to see and which any indie devs are free to use:
You play as someone who is able to perform mental time travel. This is manifested through having multiple save files which represent points in time you can travel back and forth through. So if you load a save file from 5 hours ago, your character still knows what they did in that other save file and can either act accordingly, or choose to do something else.
Some narrative uses:
Two factions are at war with each other and you have to side with one. But you need to have a save file for each route and alternate between them for things like information gathering
A village is going to be destroyed and you need to rally the people to stop it, but they won't believe you unless you helped them out 10 hours ago, requiring going back in time and gaining their trust earlier. Saving the town and letting it be destroyed both provide something of value making it a good idea to do both.
The true ending requires you to go back to the start of the game and stop the big bad at the very beginning. This unlocks a new campaign where the former big bad becomes your ally.
Some mechanics ideas:
Leveling up with a skill tree. Simplest idea is to have a fighter/mage/thief set of skills to learn. Your progress doesn't carry over between files because you aren't physically shifting. So different files can have different builds
Each ability has a proficiency level that does carry over across saves. The higher your proficiency, the lower the requirements to relearn a skill. For example, if your magic stat needs to be 20 to learn a spell, you can become proficient enough to learn it at 15 magic, but it costs more MP until you get to 20 magic because your body is still catching up to your mind.
And then the final dungeon should be in some bizarre time warp that lets you make a party of four different versions of yourself from four different save files.
