This thread is about the first derivative game of Spore... One that was put on the web in 2006, before Spore was even released.
This thing called "Watcher."
It consists of two separate projects; a Cell Stage + editor, and a Creature Editor (the latter has very unorthodox controls, so it's a bit hard to use).
What's remarkable is that it's pretty much the handiwork of a single person (Brian Buetow) who just wanted to give people something to pass the time while the Spore hype train was chugging. Not too different from Thrive's motivations. Development stopped in late 2007 with the coming release of Spore, but it's pretty neat what was made in that small amount of time.
Main Website + Download (under "Demo," but you'll have to temporarily turn off Windows Defender or whatever software you have, since the download is old, sir, and doesn't check out): sites.google.com/site/brianskis22/