I know other version control software exists, but does anyone use it? Why? What are the differences? All I've ever actually seen people use is git.
Git is definitely dominating the landscape. The fact that it is free software plays a big role. There are alternatives, but they are unlikely to gain much adoption. They may provide slightly better UX or marginally more comfortable flows, but it's not enough to replace Git. Not to mention, most developers don't even really care about which SCM they use.
Git is freaking amazing. Any current alternative is going to be a joke next to it.
People using other ones are simply missing out. SVN/CVS just need to die.
There’s perforce which is primarily used for game development. Often games have a lot of binary files that are hard/impossible to generate diffs of unlike text based files. Perforce requires you to check out individual files and prevents any merge conflicts on an individual file basis.
My experience with Perforce hasn't been really positive - especially compared to Plastic SCM, which is amazing. The merge tracking in history is such a cool feature, and it's generally really smooth to work with.
The only issue is the pricing model, which is also a reason why I sadly can't use it on many projects. Unity way too greedy and their strategy is to just acquire and paywall anything usable.
