I was reminded of this idea by a tg thread which caused me to add and change a few things with it.
In the relative future a project for a massive space station that will be used to conduct research for faster than light travel and space colonization begins. Before the project is completed a fully constructed but damaged instance of the station appears in orbit. No one knows how and the comms that should be in the station aren't being answered. A team of those skilled or disposable enough are sent to investigate this bizarre event.
What has happened is the faster than light device on the station is a device, unknown to its inventors, that distorts time instead of space. Something happened to send the station back in time during an alien invasion ironically intent on destroying the device. The aliens already have the devices and even developed personal versions but are extremely militant about its use due to a disaster in their distant past.
The station is derelict with signs of heavy combat throughout. Systems are damaged and travel between the many different parts can be hazardous in itself. The station is designed to be completely self sufficient, and is the size of a small city. The whole station is controlled by a sentient AI that already knows the party for some reason, and even has a sort of fixation on one or a few of them.
Roaming the station is an alien strike team that will largely avoid the party and bide its time to make a surgical strike against the cause of the time distortion. Also on the station are (an indefinite supply) of future versions of the PCs, the first few should definitely not be identifiable as such at first, intent on stopping the party from mucking up time in their attempt to solve everything by any means necessary. Also the general time distortion around the station will cause any number of crazy occurrences to happen. The GM is encouraged to have fun with that and keep the party paranoid.
I had a few specific ideas with types of future versions but it's probably very dependent on the PCs. One idea I want to mention is if any of the PCs try to go to the past on the alien planet to try to prevent the invasion they should be ejected back into their time line, they caused an aborted time line from all the nonsense they did and now a time refugee version of them is leading the aliens in the crusade against other species developing time devices.