Listing local users with PowerShell is easy: A reference to the local computer object can be created with $computer = [ADSI] "WinNT://." and then user and group accounts can be accessed through the Children property ($computer.Children).
There is only one problem with this: On Windows Server 2012 R2 (and also on Windows 8.1 according to here and here), the process will hang indefinitely when trying to iterate over the children. Even canceling the action with CTRL-C will not work. The only way to get out of this is closing and restarting PowerShell.
Luckily there is a workaround for this bug: When explicitly filtered for user and group objects, the children can be iterated. So before iterating over the Children property, you should configure the schema filter by calling $computer.Children.SchemaFilter.AddRange(@("user", "group")) and everything should work nicely.
PS: I would have posted this solution to the two site discussing this issue. However, both force you to register before posting anything. In my opinion this is a great way of keeping people from participating.