Pyfa

What is Pyfa?

Pyfa is an open sourced, cross-platform python-based fitting tool that includes additional tools to calculate a multitude of stats for any combination of ships, modules, skills, and other factors without having to source said parts within game.

How to Set up Pyfa

Go here: https://github.com/pyfa-org/Pyfa/releases/latest
Choose your OS and download the latest file. (for Windows, we would recommend *.exe)
Go to your Downloads and run the installer. Depending on your security settings, you may get a security warning from your OS. A suggested install location is to create a directory within your EVE folder.
Run the program.

Why do we need Pyfa?

In-game, we have various tools, such as the fitting manager. However, they are limited. Unlike the fitting manager, Pyfa can show you stats with many additional variables

Skill plans - what you have, what you are missing for a fit.
Fitting attributes with or without fleet boosts, boosters, etc.
Weapons/Miners' dps/yield with various modifiers at different levels.
Implant Sets and value variations.
Plans and fits can also be imported/exported.
And much, much more.

For more in-depth guides, consult the official Pyfa User Guides found Here or various YouTube Guides