International EPR Society
Advancing the field of electron paramagnetic resonance
The European Federation of EPR groups (EFEPR)
All necessary stuff to survive inside and outside of the lab.
Easy to use tools for radio and microwave frequency calculations and conversions.
Spin trap database
Very useful link
Another useful community
A powerful solution for those who dealing with the simulation of EPR spectra
Edmund Optics® Technical Tools. Useful calculators.