EFT (Eve Fitting Tool) is an invaluable tool for putting together ships. When used in conjunction with Eve Mon, EFT will allow you to properly fit your ship to maximize it's defensive and offensive capabilities. It will calculate speed, capacity, Max DPS (Damage Per Second) given and taken and many other characteristics.  This tool is a must have and the download below is confirmed working and virus free.

EFT Download (Version 2.8)

The below tutorial is somewhat outdated but will answer many questions one might have about EFT. A revised tutorial is currently being planned.

EFT Tutorial