Across the infinite complex of metaverses, there are a multitude of potential arrangements for timelines. Here i attempt to catalog the varieties.

In quantum timelines, there are a near-infinite number of divergences, caused by everything from rolling dice, to choosing what to wear. Timelines converge as well, when the right series of choices result in a net similarity between universes. These timelines are among the least interesting, as they are extremely malleable.

• Minecraft

In chaos timelines, divergences are only caused by events that are below a threshold of chaos. People are predictable and will do the same things, but rolls of dice will spin out and create alternate timelines.

• Community

In ripple timelines, the timeline is constantly correcting itself, removing errors and trying to trim itself down to a single chain of events. A side effect of this is that the timeline has a level of metatime; it takes time for time to correct itself. This may seem redundant, but it may make an amount of sense; the timeline does not wish to correct itself, and so it leaves time for anyone else to put things back the way they were.

• The Journeyman Project
• Back to the Future

In a key timeline, the timeline is generally immobile, regardless of what people do, even if they time travel. The timeline autocorrects to such an extent that even if you save someone, you'll have to save them again the next day or else the timeline will find a way to kill them.

That does not, however, mean you can't change it. If you work hard enough, you can perhaps get enough people together that, with great effort, you can create a divergent timeline. This is basically how the universe avoids paradoxes.

The irony here is that, even if you change the past, you aren't guaranteed to be in that timeline. You may simply enable an alternate version of yourself to have a better/worse life.

• LOST
• Fringe

A mono timeline is a timeline which never diverges. This does not mean that time travel is impossible; it merely means that any changes you cause will immediately change everything. Or perhaps, time travel really is impossible, because the causality of the universe is too tight. This does not mean that there aren't parallel worlds; just that those parallels are pretty much untouchable.

In practice, mono timelines are the easiest to work with, as they are entirely deterministic. Even if free will exists, it works better with myths and gods, as Free Will becomes Actually Worthwhile.

• Doctor Who (as best as I can tell)