The Scratch Archive is dedicated to finding information about the development of Scratch 1.0, 2.0 and 3.0 alike. From research by all sorts of different users, we've found so much already.
Please don't add any projects that aren't TSA related.
Oldest Project: scratch.mit.edu/projects/104/
(had to be reuploaded because the original got corrupted. thanks to @Paddle2See for reupload)
Oldest studio: scratch.mit.edu/studios/14/
14th studio ever!
Oldest User: @gdpr0000001
Test account that joined 7 years before Scratch's final version was finished and released.
Oldest Scratch Version: 2006 Promotional version. https://web.archive.org/web/20061116125316/http://scratch.mit.edu/
Random PDF about the Scratch Website and how to use it from 2006. It has a lot of beta screenshots:
February 17th, 2020:
Scratch's Studio URL is scratch.mit.edu/mystuff/#galleries, suggesting that studios may have been called Galleries in an older build.