Admin Tools Test Wiki
The Admin Tools Test Wiki is a sandbox wiki that offers free testing of administrator and bureaucrat permissions. Any new registered accounts are automatically granted admin rights upon their first edit, and bureaucrat rights will be granted upon request. The wiki also uses the SocialProfile extension for all of its user pages, although this can be changed per user.
The major negative is that many sysadmin or steward assign checkuser rights to themselves without a reason specified. Users should keep this potential problem in mind when testing the tools on this wiki.