This is a disassembly/reassembly of Jet Set Willy for the BBC Micro.
jsw1.a
jsw1.5.a
It is based on a previous disassembly http://www.level7.org.uk/miscellany/jet-set-willy-disassembly.txt which is slightly different from the binary found on the bbcmicro.co.uk website (Perhaps the differences are down to a disk vs cassette version?).
This code assembles (using the ACME assembler) to create a byte for byte identical copy of the game as found here http://www.bbcmicro.co.uk/game.php?id=439