These are the main Adobe Photoshop versions. However, other Adobe editions that can be found are the Photoshop Elements series. This series was designed to target hobbyists, rather than professionals, and so runs at roughly 1/6th the cost of other editions. The series was originally introduced along side of version 7.0 and lacks many of the features found in the more professional series.
Other, less well known Adobe Photoshop versions include Premiere Elements and Lightroom.