This page contains a list of neat Development Tools for Software Devlopment, Homebrew, and Game Hacking.
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Graphics editor for the NES, as well as SNES, Genesis, and most other systems before the DS era.
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An assembler for the NES, mainly used to make custom programs. It's the one used and bundled with the Nerdy Nights NES Tutorials, so i'd say it's pretty good.