Recommended and mentioned products
Fast and Friendly Git Client for Mac
I'm a huge fan of git fork  on windows (or mac). Looks good, never failed me and does everything I need (branching, merging, rebasing, cherry picking, blaming and it can even show lost commits with reflog). And it performs really well (in contrary to sourcetree).  https://git-fork.com/.
GitHub Desktop is a seamless way to contribute to projects on GitHub and GitHub Enterprise.
The Git interface you've been missing all your life
While GitUp is a GUI app, and only available for macOS, I think it's worth noting that it has some great undo/redo capabilities built in. From what I understand, some of them were more feasible to develop because they implemented their own plumbing (GitUpKit), instead of relying on the official git plumbing. https://gitup.co/.
Simple terminal UI for git commands.
I've said this in other threads but I'll proselytize here as well. I really started to grok git after using the lazygit terminal UI. I think it's really handy to see what the current "state" of git is in and how to browse it easily. Would continue to recommend. https://github.com/jesseduffield/lazygit.
Gitless is an experimental version control system built on top of Git.
I agree that collaborative text editing between multiple users simultaneously is hard. That doesn't mean that Git couldn't have a much better UI for this problem than it does. And while I agree that Git seems to have mostly won over SVN and Hg, it doesn't follow that it's because of its UI. (For example, I think that a lot of Git's success actually comes from the UI of GitHub, not Git itself, but I don't have...
TortoiseGit is an easy to use client for the Git distributed revision control system.