A testing tool to fake privilege separation
Some projects, such as a file server, need privilege separation to be able to switch to the user who owns the files and do file operations on their behalf. uid_wrapper convincingly lies to the application, letting it believe it is operating as root and even switching between UIDs and GIDs as needed. You can start any application making it believe it is running as root.
seteuid(2)and related calls and simulates them in a way transparent to the application
setgid()calls will work, even as a normal user.