ucspi-ipc implements D. J. Bernstein's UCSPI protocol in the Unix domain, making it trivial to set up clients or servers on Unix sockets. ucspi- ipc comes with utilities using credential passing on Unix sockets, which are designed to act like a fine-grained and efficient sudo without the need for setuid programs.
ulock locks the entire virtual console system, completely disabling all console access. It gives up these locks when either the password of the user who started ulock or the root password is typed. It is able to invoke any program (i.e. a screen saver), which will be terminated on any keystroke. The idea of the program was taken from Michael K. Johnson's vlock.
userchroot is a small program which, in addition to doing a regular chroot, will also switch working directory once in chroot and drop privileges back to pre-suid values. It is intended to ease constructing chrooted user-driver services (running stfp-server in a restricted namespace for example). In order to conserve system resources, it is implemented in C. This makes it more suitable for higher load scenarios than scripts.
userv is a Unix system facility to allow one program to invoke another when only limited trust exists between them. It is a tool for system administrators, who often find themselves with a program running as one user which needs to be able to do certain things as another user. For example, the author's machine's news system needs to scan its users' newsrcs to ensure that the right newsgroups are fetched. Before userv that part of the news system had to run as root, and clumsily use `su'.