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
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