Although the majority of items at Al Kossow’s bitsavers.org are scanned copies of manuals, he also has software in source and/or executable form for a variety of machines (scroll down to “The Software Archive”) . Some of the oldest include MIT’s TX-0 and DEC’s PDP-1.
His manual collection also includes scanned copies of source code listings for some historic machines, including MIT’s Whirlwind and The University of Illionois’ ILLIAC I (scanned from hardcopies belonging to Wayne Lichtenberger).
Al notes that David Green is writing a simulator for the version of the ILLIAC built at the University of Sydney.
Updated TX-0 and PDP-1 URLs following a change at bitsavers.org.