Beware, for I have known more than one person be addicted to that game to the point it adversely affected their degrees!
Not a remake, nor open source, but the Flash adventure game "The Terrific Menace of the Invaders from Audio Galaxy" (I'm not typing that again!) is reminiscent of the Lucasarts classic Day of the Tentacle (these days playable using ScummVM). It is, of course, free to play.
Remember Shadow of the Beast? I loved that game, and the follow up (Shadow of the Beast II, of course). Somebody started remaking it in 3D! Sadly it doesn't seem to be headed anywhere (last updated 2 years ago) but I live in hope.
(Y'know, I swear I'd mentioned that last one before but Google says I haven't and I'm not reading 100 posts to see if I did!)
I'll finish off with a Super Mario remake. Since the Secret Maryo developers only provide source packages for Linux, I created some Secret Maryo 0.99.5 packages for Ubuntu Feisty Fawn (might work on Dapper Drake). Enjoy!
Franke, Neumann - Criss Source (Titan Remix)