Thinking About Time Travel RPGs
It occurs to me that one of the genres I've not gamed in for years is that of time travel. I'm pretty certain I've had the occasional time travel adventure but I'm thinking more a game dedicated around time travel. I had a Star Trek game about a starship that bounced from one parallel universe to another that was rather fun, but that was in the late 1990s/early 2000s - nothing since then as far as I can recall.
That's a bit surprising, as I love both the time travel genre and history in general. I think one of the things that makes it challenging is how to handle such things as paradox. The game I'm most familiar with as far as handling situations like this is Pelgrane Press' Timewatch which makes paradox a gameable mechanic. It's in your best interests to avoid outright paradox while dancing around it. For example, if your characters were to be imprisoned, it would be quite the paradox to have your characters just vanish from their prison cell. On the other hand, if your characters were to happen to find a key that been hidden by your future selves... Well, still a paradox perhaps, but not as bad.
Doctor Who is a bit less concerned with complexities such as paradox, with the show itself less than consistent about what they involve. The modern show has been a bit more consistent than it had been in its original incarnation, embracing the idea of a "fixed point in time" - something even a Time Lord would be unable to change - though not for the Doctor's occasional attempts, such as seen in The Waters of Mars.
Timemaster from the 1980s is a clear ancestor of games like Timewatch, featuring PCs whose mission it is to preserve the timeline - as well as, if memory serves, parallel Earths' timelines as well. Though it has been ages since I read through it.
Were I to do a time travel game today I would probably discuss with my group what they were looking for - if they were more interested in the adventure aspect Doctor Who might be more appealing whereas a game which embaced things like paradox would steer me towards something like Timewatch...