Ceph

To make commands and their usage discoverable and easy to look up, each subsystem could provide a help command
that listed each subcommand (and maybe its arguments?). Longer usage could then be obtained with an argument to help. This could look something like:

$ ceph help
Usage: ceph SUBSYSTEM COMMAND [ARGS...]
SUBSYSTEM may be one of:
mds
mon
pg
osd
...
$ ceph help pg
Available commands (use "ceph help pg COMMAND" for detailed information):
dump [--format json|plain] [epoch]          retrieve information about all placement groups
set_full_ratio ratio                        update the threshold at which the cluster stops accepting I/O
...
$ ceph help pg dump_stuck
<full usage info here>

For things like 'ceph osd tell', an arbitrary osd could be queried, or 'ceph help osd tell N' could be accepted.