Tailscale is written in Go with lots of dependencies. It also has a lot more features, to the point some would call that too much 😅 Zerotier is pretty lean and in C. That would explain those 55 MB idle memory usage difference. But those 245 MB after iperf3 test though... I can't explain, but it's consistent and repeatable.

Netbird uses kernel Wireguard module, right. Is there a way to measure kernel memory / CPU usage attributed to Wireguard? Zerotier, which has the lowest memory usage, does not use Wireguard at all, they have their own custom protocol and it's userspace AFAIK.

I might just compare free output before / during / after iperf3 test. Will do that later today.

UPD: done

After 10 minutes PSS was back to ~74 MB