Strange user named "Other…" on 10.6
"Other" is not a user. It just allows you to enter a username and password into textboxes instead of clicking on an icon. 

It can be used to connect to a network domain user. It can also be used for special users, such as "Root" (which gives you unlimited control over all hidden and restricted files) and ">console" (which logs into your Mac in command-line-only mode.)