Somebody's writing a clean-room implementation of Solomon's Key for the NES. All of the original levels are already implemented. Theoretically cross-platform. Doesn't quite work yet but it's getting there. Includes a level editor so you can build your own levels. Seems to have some tricks to getting it to run but I haven't tried them yet.
A company that makes cases for the Raspberry Pi that look like classic gaming consoles, like the NES. They sell them through Amazon. I have a few, and they're quite nice.
A collection of free homebrew games for a number of (emulated) systems, packaged for easily running on a Retropie.
The source for all your NES programming needs.
Header-only NES emulation library with an easy to use API. Include the header and instantiate the emulator with a handful of lines. Seems a fully featured NES emulator, capable of running even later games like SMB3. MIT licensed.
An online password generator/decoder for the Mega Man games, Castlevania 2, Metroid, Solar Jetman, the Guardian Legend, Faxanadu, and Battle of Olympus. Pick the options you want and it'll build you a password. Type in a password and it'll show you what it means.