If you want an entirely free video editing suite with cropping tools, Kdenlive is one of the best. It's also completely open source, so you can modify it, tweak it, dig into its codebase and see how it all works – it's entirely vettable and customizable how you like it.
This multi-track video editing tool makes it quick and simple to crop video. Using its effects menu, you have a range of cropping options, including zooming, edge cropping, and cropping to the individual pixel, letting you adjust aspect ratios and focus in one go. KdenLive also includes versatile audio effects, and has a powerful theme system which lets you customize the look and feel of the software to your tastes.
It doesn't offer GPU rendering, so if you were planning to use heavy video effects, you'll want a powerful CPU to render quickly. It's also missing a few key output file formats, like MKV, MOV and AVI. Otherwise though, it's a great program to crop video with.
Pros
Cons
No GPU rendering
Limited output formats