The "leaves" command:

Usage: fossil leaves ?OPTIONS?

Find leaves of all branches.  By default show only open leaves.
The -a|--all flag causes all leaves (closed and open) to be shown.
The -c|--closed flag shows only closed leaves.

The --recompute flag causes the content of the "leaf" table in the
repository database to be recomputed.

Options:
  -a|--all         show ALL leaves
  --bybranch       order output by branch name
  -c|--closed      show only closed leaves
  -m|--multiple    show only cases with multiple leaves on a single branch
  --recompute      recompute the "leaf" table in the repository DB
  -W|--width <num> Width of lines (default is to auto-detect). Must be
                   >39 or 0 (= no limit, resulting in a single line per
                   entry).

See also: descendants, finfo, info, branch