In my daily life, I am employed as a senior software engineer and work mostly on complex back-end systems, but also occassionaly on front-end web projects. My favorite programming language is Java, which runs on the beloved Java Virtual Machine, but I use all kinds of programming languages, from the more popular to some quite obscure ones. I greatly prefer working with the tool that's the right for the job.
I also work on some projects in my spare time. Sometimes just to try out an idea that's playing in my mind. Sometimes to just to get to work with a certain programming language, platform, framework, library, technology and/or tool.
Pet projects are a very good way to sharpen your technical skills and to get to work with newer (and/or older!) technologies, giving you an edge and a broader view of what is available and how to incorporate new technology in code bases, than those that only use the computer for work.