Games with released demos, but cancelled?

Spyros Kingdom for PC.

The developer had the demo on their site as a download for a while. It was cancelled when another developer approached activision with a prototype that would eventually become Skylanders.

 

Should check out these 3 videos on YouTube;
Dennis Quaid (Michael Swift) Interview
Nick Chinlund (General Mitchell) Interview
Michael Ironside (Professor Krone) Interview

Those interviews are clearly from before the redesign and recasting of Michael Swift (voiced by Greg Grunberg in the final, the guy who played the psychic cop in Heroes). Gives at least a tiny window into the original expanded plot and stuff.