What kind of completions do you mean? PowerShell has completion for commands, parameter names and arguments. You can define arbitrary script blocks to do custom completion (or for simple cases just use `ValidateSet`). They can be defined either in the script/function itself, or separately with `Register-ArgumentCompleter` (that also works for non-PowerShell programs).
ls -l
-1 (List one entry per line)
-A --almost-all (Show hidden except . and ..)
-a --all (Show hidden)
-B --ignore-backups (Ignore files ending with ~)
…and 51 more rows
In Powershell, if I type Get-ChildItem -<tab>
It just cycles through options apparently abitrarily. The first suggestion is "-Path", and it offers no facility to provide explanatory information.
In principle there isn't anything that would stop one from making that. PowerShell has history info available, and help messages/docstrings can be given for parameters (`Get-Help command -full` will show them if available).