The Saturn PCB Toolkit is a handy freeware tool for PCB design-related calculations.
It is particularly useful for helping us find a starting point for controlled-impedance traces for RF and differential signals, such as RS-485. Impedances for traces such as differential pairs, microstrips, striplines or coplanar wave are easily calculated by referring to a visual layout and entering appropriate values.
Other convenient calculators include those for finding capacitor/inductor reactance, thermal resistance, wire gauge parameters, among others.
Check it out at http://www.saturnpcb.com/pcb_toolkit/
