I usually have a couple of projects to work on in my free time. Most of them are from ideas that i think would either make my life easier or more interesting.
Others are just for the sake of learning something new or for the fun of it.
The Openhab server is one example of both, it was interesting to learn how different devices could communicate with the server and the finished project is really useful day to day.
Different projects familiarized me with different programs and programming languages. Testing different programs taught me how to use VirtualBox as a sandbox, I got to use Wireshark a lot more when figuring out some network connected devices and when i needed a simple GUI for a project I took a shortcut and used a webinterface with html, css and Javascript.

Below are some of the programs i often use in my free time: