RText started as a program for me to cut my teeth on Swing programming. It was a simple Notepad clone. Then I started thinking of all the many features that Notepad doesn't offer that are extremely useful in a text editor, so I started adding those as well. Eventually, once I wrapped my head around how the Swing text package worked, I was able to add in syntax highlighting. That's where the project really started taking off, as suddenly became much more useful for me at my job. I work on many different OS's every day, so having a cross-platform tool is very handy to me. My goal then became to make it a robust, full-featured programmer's editor that wasn't as heavy as something as Eclipse.
A lot of the focus these days is on the editor, RSyntaxTextArea. I know that there aren't many high-quality, open source options for syntax highlighting text components in Swing, so I broke it out into its own project. Since then I've been getting a fair amount of email from users with suggestions for tweaking the editor, making it more usable and robust as a stand-alone library.