Unknown to many the program Blender, which is better know for 3D development includes a full sequence editor (nle). Like the rest of blender it has a highly ideosyncratic interface and either you like it or you don't (I do). Many basic functions aren't documented anywhere, but with a little imagination it can be made to do just about anything. What follows is an unorganized list of tricks I've worked out. This is not a place to get started. For that I recomend Eugenia's starter guide and the official documentation.

Many plugins can be found to expand the power of the sequencer, but there are some strange omitions, so I've written a couple of my own. They can be found on my plugins page.

Letterboxing
Those black strips you see at the top and bottom of a movie sometimes are called letterboxing and at time's they're a necessary evil. You'd think this would be a basic feature but I'll be damned if I could find it anywhere, however there's a pretty simple way to do this. For example I will be letterboxing a 640x360 video to fit in a square 640x480 final image. First I change my output resolution to 640x480. The image looks stretched out now, but that's ok. Now I select all my video segments and filters and click "m" to create a meta strip. Then in the sequencer window with the meta strip still selected I click on add->effect->transform. In the transform options I change yScale End to 0.75 (360/480) and et viola, I have a letterboxed final image.

Color correction
Doing color correction is actually pretty straight forward. Select your clip, click on "use CB". Set gamma to inverse then click on the white triangle. Click on sample and click the little eyedroper on something white in the frame and like magic all your colors (should) be correct.