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.

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.

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.