In keeping with my "abuse of the theme" motif, I present NES Quest, because programming for the NES is like sacrificing your sanity.
This is not a complete game: my ambition exceeded my preparedness and the available time, but this is a playable demo.
Quest through the land, searching out and collecting the components to repair your NES: Find the 6502 CPU, the PPU, the RAM chip and the 7404 Inverter.
Watch out for Spiders, Grumps and Skulls. Grab a sword to defend yourself.
NES Quest draws a lot of inspration from The Legend of Zelda and Gauntlet.
As an unfished game, the RAM and 7404 Inverter are not present in the game. There is no win condition, goals and the player doesn't have a health system.
The movement and combat system need some fine tuning to feel more playable.
This game utilizes the MMC3 mapper and sets the mirroring the the little used Four-Screen mode, wherein the cartridge provides additional RAM to give 4 screens worth of video memory (I think only Gauntlet and maybe one other game used this option).
The game creates a split-screen effect by using the MMC3 IRQ to create an interrupt 192 scan-lines into the display, and then reprograms the scrolling registers to the location of the status display. This doesn't seem to work correctly on a real NES - I'm not sure why yet.
MMC3 is configured such that $C000-$FFFF is mapped to the last two banks (a rather standard configuration), and $A000-$BFFF is mapped to the 3rd from last 8k bank. The $8000-$9FFF region is remapped as the player progresses through the game to provide additional level data.