For most part, I will just work with any software that gets thrown at me. But there are some tools that I prefer over others. This list might grow and change over time
Videolan player all the way. Since the turn of the millenium or something :-) Runs on any desktop operating system I can think off. Plays any movie format you throw at it. Without external libraries. Has been amazing al those years.
Although I have licensed copies of other office suites, I still prefer Libreoffice, because it will work for me on any desktop operating system I can come up with!
Although a lot of different mail clients have some perks that I like, I mostly rely on Betterbird since last year. It is a Thunderbird fork that has more polish and bugfixes than the upstream version.
The things I really like is the cross-platform aspect and the S/MIME + GPG integration that works well enough.
For any serious firewall setup, I try to rely on OpnSense. Very nice WebUI, lots of features that just work and proper open source. OpnSense