> And picking source and destination commits for a rebase is much easier visually on the commit graph than making note of hashes on the command line.
In git branches are more comparable to hg bookmarks and used so heavily it feels very rare from the command line where you would directly use a hash rather than a branch name.
> Related question: does anyone know of a good git GUI that works on Windows and Linux? (Ideally, but not essentially, free.)
If you are happy with the Tortoise family there is a TortoiseGit [1]. I think the Tortoise "family" still shows its roots in SVN much too often to be a "great" Git GUI, but it should certain feel comfortably familiar. Though like TortoiseSVN, TortoiseGit only supports Windows. It's interesting that TortoiseHg was the only one in the "family" to invest in cross-platform.
GitHub Desktop can be a useful cross-platform GUI sometimes, especially for somewhat less code-focused folks. While it puts GitHub front and center, it's still a general purpose enough tool.
Git has an "okay-ish" cross-platform GUI that is almost always bundled with it called "Git GUI". I don't know a lot of people that recommend the main interface for Git GUI, it's an ugly Tk-based throwback, but it does cover almost all of the basics of TortoiseGit without as much direct shell integration. (It has some bare shell integration into the right-click context menu as an optional checkbox buried in the Windows install at least.) On the other hand, while almost no one uses the main commit-oriented parts of Git GUI, its commit graph viewer `gitk` (which is almost always available in the PATH by that name) is almost an almost indispensable power tool, and I think still the commit graph tool to beat for git. `gitk` is great, and years ago became my muscle memory over `git log` for a lot of situations.
At this point the most common cross-platform "GUI" I use day-to-day with git though is just VS Code. It's built in git support is sufficient for a lot of work, and there are some useful, optional power tool extensions like "Git Lens" that make it even better.
[1] https://tortoisegit.org/