The history of Paint.NET is an interesting one: it began as a senior project at Washington State University a mere three years ago, intended as a sort of successor to the built-in Paint program for Windows. Its lifespan ended up being far longer than a single semester, and it gained additional developers. It’s not technically affiliated with Microsoft, but it was mentored by Microsoft employees (the benefit of being near Redmond, I suppose).
Now, two students who worked on Paint.NET in college, who have now gone on to work at Microsoft, continue to develop the program as an open source project (MIT license).
I’m glad that the filthy taint of Microsoft hasn’t brought this project within its proprietary folds and turned it into crap, because I actually like this program more and more every time I use it. It’s written in C#, intended for the .NET platform (2.0 required right now, but 3.0 in the future, I believe). This means it’s not exactly a speed demon, but when I tested it, it used about 45MB of system memory fairly consistently, and wasn’t too sluggish.
The 3.0 version of Paint.NET, which was just released, might not have been an entirely new paradigm, but it does bring some excellent new features to the fold. I can’t compare it, apples-to-apples, with v2.0, because I didn’t really use it prior to this.
However, if you don’t feel like pirating Photoshop, and you don’t like the GIMP (and who really likes its horrible interface?), then Paint.NET is the perfect middle-tier bitmap editor for you. It sports a new tabbed interface (open files are displayed as thumbnails along the top of the program window, which I think is a really intuitive way of doing things). Its tool windows sport a really great transparency effect that makes them translucent when not in focus, meaning that they don’t totally obscure the document like they do in Photoshop.
One of the best new features, I think, is the gradient “draw,” which is a feature I have yet to see anywhere else. It’s a flexible, tool-based gradient draw that’s organic in nature: you click and drag, and a gradient is drawn and rotated based on your mouse movements, but not committed until you release. It’s a really nifty feature.
Long story short: if you don’t need the power of Photoshop, and you don’t mind .NET, then Paint.NET is a really wonderful program.