None of the software which developers build and maintain today would be possible without open source software. Personally, I have made it a habit to contribute to open source projects I use. Before deciding to use an open source library, I usually clone the repository, inspect it, and if I find something worth fixing, I fork, and open pull requests. This gives also a great opportunity to find out about the project and the community around it.
Apart from contributing to open source projects, I also maintain a few small projects:
If you want to find out more about which open source projects I contribute to, find me on GitHub.