

KiCad takes around 5 minutes to learn and is some of the best software for designing schematics and PCBs.
Falstad is great for when you need simulations of schematics and don’t want the headache of trying to use KiCad’s built in simulation tools.
Both are FOSS.









It’s not a black box since it’s FOSS, but it is indeed monolithic.
I still use systemd since I find it easy to work with and I’ve been using it for many years.
It’s also worth noting that the Linux kernel itself is monolithic and does not exactly follow the UNIX philosophy, but I’m not aware of any stable microkernels with the same level of functionality as Linux.