OZ (Ultimate Marvel)
OZ is a fictitious artificial mutagen responsible for the creation of the Ultimate Marvel Universe's Spider-Man, and several of its other characters. The writer, Brian Michael Bendis decided that a genetically mutated spider would be the source of Peters power, rather than a radiated one, to update Spider-Man for the 21st century.
Read more about OZ (Ultimate Marvel): Origins, Peter Parker (Spider-Man), The OZ Explosion, Mary Jane Watson