git rev-list --all --parents | grep "^.\{40\}.*<PARENT_SHA1>.*" | awk '{print $1}'

    fossil timeline after <COMMIT>

Also, a cursory test in a local git repo just now showed that command seems to print out only immediate descendants--i.e., unless that commit is the start of a branch, it's only going to tell you the single commit that comes immediately after it, not the timeline of activity that fossil will--and all it gives you is the hash of those commit(s), with no other information.

I use git myself, not fossil, but if this is something you really want in your workflow, fossil is a pretty clear win.

How many other ways of looking at commits or trees are there, that are hard in git but impossible in fossil because the author didn’t feel like it?

You could alternatively use:

    git log --graph

  git log <COMMIT>..

  git log --all --ancestry-path ^<COMMIT>

Half the time, when I know what I want, I both keep forgetting git flags and sub-commands - and struggle to find them in the man pages.

Like the fine:

git diff --name-only # i list only the files that are changed. But I'm not --list-files.

    git diff --stat