pdksh is the ''public domain Korn shell'', a clone of the Korn Shell. It has most of the ksh88 features, and almost none of the ksh93 features.

The last version, [http://web.cs.mun.ca/~michael/pdksh/ pdksh 5.2.14] from 1999 July 13, still has several bugs. Systems like [http://packages.debian.org/sid/pdksh Debian], [http://www.openbsd.org/cgi-bin/cvsweb/src/bin/ksh/ OpenBSD] and [http://cvs.pld-linux.org/cgi-bin/cvsweb.cgi/packages/pdksh/ PLD] now apply several patches to pdksh.

• If an example from Rosetta Code "works with pdksh", then someone might have tested the example with one of these patched versions of pdksh.
• If a #!/bin/sh script "works with pdksh", then the tester might have used OpenBSD, where both /bin/ksh and /bin/sh are pdksh.

mksh is a successor to pdksh. mksh consolidates several patches and a few new features into one shell. If you want to install pdksh, then you might instead install mksh.