NES++ is a modchip for the Nintendo Entertainment System (AKA NES). It has the following features:

• Reset-From-Pad (AKA In-Game-Reset AKA IGR): Press Select + Start + A + B.
• NESRGB on/off toggling and palette switching:
  • Control your NESRGB add-on board: turn it on or off and set your palette of choice from the Player 1 controller pad: Press Select + Start + Down to turn it on/off or Select + Start + Left/Right to cycle through palettes.
  • Alternatively, palettes can be switched through the Reset button: Keep pushed.
  • The mod is switchless, so you don't need to modify the aesthetics of your console installing ugly switches.
  • The last used palette is automatically saved and reused at power up.
  • Supports a single led, common-anode or common-cathode dual or RGB LEDs to indicate the current mode (Almost any color can be used when PWM pins are available).
• CIC on/off toggling: So you want to play games from a different region, but you already feel nostalgic for that blinking power led? No problem, just turn your NES's CIC chip on or off at will through the Reset button, just quickly press it twice or through the Player 1 controller: Press Select + Start + Up.
• Uses cheap Atmel AVR microcontrollers.
  • Can be flashed on different chips (ATtiny's, ATmega's, or even a full Arduino board).
• Even though default settings are recommended, everything can be customized to taste.
• Uses the popular Arduino environment, allowing for easy development, testing and modifications.
• Last but not least, it is Open Source and Free Software!

Note that there is also a NES emulator named nes++, but it is a different project. I chose to use that name in analogy with my MegaDrive++ project, and since the emulator hasn't been update in a while, no confusion should arise.