Good Network Simulators for Research?

I've been trying to find some network simulation software to play around with networks and software I've been writing, as I can't reasonably recreate these sort of networks irl. Preferable something cross platform (windows and linux) and free, although I wouldn't mind paying if it's good. I also want to be able to simulate WAN and other non-ethernet networks.

Closest free tool I found, was gns3. Unfortunately, I found it too unreliable and buggy to use. I've seen other products very close to what I want but don't sell to consumers and probably are way to expensive anyway. Most other software I've found seems to mostly be Cisco certification tool and focused more on education.