Romhacks:

• Link to the Past Randomizer - Generates a shuffled ROM with all chests and items swapped around, sending you on a wild goose chase through Hyrule trying to find everything required to beat Ganon. Has a LOT of settings to play around with.
• Link to the Past/Super Metroid Combo Randomizer - Like the above, but with both games combined into a single ROM using some elaborate witchcraft. Certain doors take you from one game to the other, and the item pools are shuffled together so you'll have to go back and forth between Hyrule to find Metroid items and Zebes to find Zelda items. It's a bit imbalanced by the fact that LttP is a much bigger game than SM with far more items and locations, but I recommend playing through it once for the sheer novelty.
• Celeste Mario's Zap & Dash - A metroidvania running in SMB1's engine. As the name suggests, it's heavily inspired by Celeste and ports in mechanics from that game.

Standalone fangames:

• Panel Attack - Open source clone of Panel de Pon/Tetris Attack/Puzzle League/Puzzle Challenge/oh my god Nintendo please pick a name and stick with it featuring netplay and modding support.
• AM2R - Another Metroid 2 Remake. Do note that I've heard a big 2.0 update is supposed to be coming soon, so you may wish to wait for that.