Glitch was a web-based game written by Tiny Speck Studios, who would later go on to make Slack. (The same team originally worked at Ludicorp where they were part of the team that made Flickr.) It was a platformer with an emphasis on crafting, collection, exploration, and community.
The art had a definite Dr. Seussian element to it, and the music sticks in your head well enough that here it is 2017 and I just had one of the background songs stuck in my head, prompting this node. It originally opened in 2011 and closed down in 2012 due to "lack of interest." They released all of the ActionScript source code to the public as well as the music and art under a Creative Commons CC0 license. (Though, I suspect it had more to do with the company looking at the cost of maintaining a Flash game compared to something that they could generate profit from, reality ruins everyone's fun!)
There have been attempts to remake a fan version with both Children of Ur and Eleven, but nothing has quite captured the strange alchemy that was the original game. Part of this is that their focus on creativity and cooperation made the community a large part of the draw, and it's difficult to reassemble that from source code and the creative commons art. In much the same way that E2 would be a hard phenomenon to recreate, even with all of the component pieces. Once it's released, it's hard to get that magic smoke back in the box.
You can still see the list of former players and all of the objects at their website http://www.glitchthegame.com
EDIT: Oh! Very excited, the Slack client that we use for work had a problem, a "GLITCH" which displayed an error screen where the background was a scene from Glitch the Game. What a wonderful easter egg!