Now in its 13th version, Adobe Photoshop has become an indispensable tool with 23 years of features and cruft baked into it — but the source code for the application's original 1990 version is now available as a free download. The Computer Science Museum is offering the source code for Photoshop 1.0.1 for the Mac with Adobe's blessing. It's for non-commercial use, though it's not something you're going to be able to run out of the gate — aside from operating system and architecture issues, the MacApp libraries that were licensed from Apple at the time are not included. It consists of about 128,000 lines of code, the majority of which were written in the Pascal programming language.

As the Computer History Museum writes in a blog post, Photoshop began life in the 1980s as a program called "Display," written by Thomas Knoll. His brother John Knoll — a visual effects veteran that has worked on everything from The Abyss to the upcoming Pacific Rim — used it to edit photographs. Adobe struck a deal to distribute a version of the application in 1989, and Photoshop started shipping a year later. If you'd like to check out the humble beginnings of what has become a truly iconic piece of software — or browse through its manual, for that matter — the downloads are available now.