Toontown Release Notes are information posted on the Toontown Website. They provide information on what has been updated and when, from minor bug fixes to the adding of entire playgrounds. The original Release Notes can be found here on the game site (external link).
"Open Server" is the name given to the publicly available version of Toontown.
The index below links to the release notes for each year of Toontown.
Test Server refers to the limited access server(s) for testing purposes of enhancements/new features.
Test Server Release Notes closely align to the Open Server notes, but also reflect subtle changes as the different issues were worked on.