I just enjoy writing software, so in my spare time I have created a number of projects which are free and available to download. I also use a lot of this software in my day job.
Creating software on your own terms is a joy, as it lacks the requirements and constraints of commercial development activities. It also pushes you to get out of your comfort zone, learn technologies and techniques that you wouldn't normally learn, and helps you engage and communicate with your peers.
For any developer that has not yet published any software or contributed to other people's projects, I would highly recommend it! Here are some of my projects: