All the designs on this site are currently using Eagle 5.3. Eagle is a multi-platform package, and will run natively on Linux. It is not Open Source. A free version is available for smaller designs.
I prefer Eagle as it is multi-platform capable. I have considered using KiCad, but in the effort of time and software familiarity have used Eagle. Other software, such as Pulsonix and DipTrace is Windows only and not an option. OrCad, Altium, PADS and Allegro are simply too expensive.
A bit of suffering saves a lot of money :)