A public domain version of the Korn shell

 PD-ksh is a mostly complete AT&T ksh look-alike (see NOTES file for a list
 of things not supported). Work is currently underway to make it fully
 compatible with both POSIX and AT&T ksh (when the two don't conflict).
 .
 Since pdksh is free and compiles and runs on most common Unix systems,
 it is very useful in creating a consistent user interface across multiple
 machines. For example, in the CS department of MUN, pdksh is installed
 on a variety of machines including Suns, HPs, DecStations, PCs running
 Linux, etc., and is the login shell of ~4500 users.