Login.app is an XDM like graphical login program that will give you a sleek looking interface to *nix. It can be configured with different background images to suit your tastes.

wdm is the WINGs Display Manager (written using the WINGs toolkit by Alfredo Kojima, Window Maker author). Basically, it's a modification of the XFree86 xdm package for graphically handling authentication and system logins.

Postilion tries to be a clone of the NEXTSTEP(tm) Mail.app. It uses TCL/TK and is based upon the popular TkRat program. It includes support for MIME, virtual folders, PGP, unix mail files, MH folders, POP, and IMAP. Great effort has been taken to support multiuser environments using system wide configurations, mailboxes, addressbooks, etc.