Arkham Development released some projects in open source:

• All Arkham PC demos written in Basic and x86 assembler (from 1991 to 1998).
• One Arkham Amiga intro and an unfinished Amiga demo written in 68020 assembler.
• A full 3d engine.
• Arkham demo PC tools (paint program, sound tracker, modeler, picture and 3d converters) written in Basic and x86 assembler.

You can access to the sourceforge project here.