I've recently started working on a Mario Fangame that I'm calling Super Shroom Bros. It has similar gameplay to Super Mario Bros on NES except the main character is the Super Mushroom, who has to save Mario after he and peach get kidnapped by Bowser.
Here is a short little clip of my prototype:
I plan to finish this game and release by this in several weeks (April 1st perhaps?). Hopefully I'll release a demo soon.