You mention Linux in the last part of your question, but since the title is generic I'll answer for FreeBSD.

FreeBSD has similar commands as Linux but they are commands passed to the `pw` utility: 

 pw useradd [user|uid] ...
 pw usermod [user|uid] ...

and so on. However, one can parse the command into two parts: `user` and `mod`; a noun and an adjective. Moreover, one can also use `group` and `del`:

 pw groupdel [group|gid] ...

to, for example, delete a group. So here's what I think is really cool: **the order doesn't matter, nor does the spacing!** What this means, is that you can remember what to call by thinking about what you want to do (in English anyway):

 pw del user [user|uid] ...
 pw mod group [group|gid] ...
 pw show user [user|uid] ...
 pw next user [user|uid] ...

and more! The `pw` utility also lets you lock and unlock accounts:

 pw lock [user|uid] ...
 pw unlock [user|uid] ...

Options and any parameters that you pass are all standardized (although don't always apply to call commands) so memorization is minimized. All in all a nice way to do things.

*Note: the ellipses in the above examples represent options and paramters passed to `pw` not additional users or groups.*