You will find below some links to Apple IIgs Video Games (or Demos) Source Code written in assembly language (use Merlin 16+ to re-assemble the source code).
Even if each game engine is specific, you may find there explanations about how games were made and grab there few parts of code (Music Player, Boot Code, ...).
We will update this list if we can find extra titles to add there.
- Games using Prodos 8 :
o Rastan http://www.whatisthe2gs.apple2.org.za/rastan
- Games using GS/OS :
o Blockade http://www.brutaldeluxe.fr/sourcecode/blockade.html
o Cogito http://www.brutaldeluxe.fr/sourcecode/cogito.html
o LemminGS http://www.brutaldeluxe.fr/sourcecode/lemmings.html
o The Tinies http://www.brutaldeluxe.fr/sourcecode/thetinies.html
- Games using Custom OS :
o Blue Helmet http://www.freetoolsassociation.com/detail_description_Blue_Helmet.html
o Bulla Demo http://www.freetoolsassociation.com/detail_description_Bulla_Demo.html
o Oil Landers http://www.freetoolsassociation.com/detail_description_Oil_Landers.html
o Space Harrier ftp://ftp.apple.asimov.net/pub/apple_II/images/gs/programming/fta_code/GIFT2.SHK
- Demos using Custom OS :
o ACS Demo ftp://ftp.apple.asimov.net/pub/apple_II/images/gs/programming/fta_code/GIFT4.SDK
o Modulae http://www.freetoolsassociation.com/detail_description_Modulae.html
o X-Mas Demo ftp://ftp.apple.asimov.net/pub/apple_II/images/gs/programming/fta_code/GIFT5.SDK
ftp://ftp.apple.asimov.net/pub/apple_II/images/gs/programming/fta_code/GIFT6.SDK
ftp://ftp.apple.asimov.net/pub/apple_II/images/gs/programming/fta_code/GIFT7.SDK