From the NAGI Website:
NAGI was created by disassembling the original AGI executable and writing equivalent C code that would run under SDL which is a free generic library for low-level access to graphics and audio. It can read both v2 and v3 game data for the PC.
I started working on this (disassembling and learning stuff) around November 1999. I didn't really do much work on it until the start of 2001 when I finished the picture rendering code. So I started with a program that draws agi pics to this... I actually got the initial idea from the guy who recreated an old game called Digger . He did the same thing by disassembling the original game and recoding it all in C.