Scribus — Desktop Publishing (http://www.scribus.net/)
I mainly use Scribus for the internal layouts of my books. It handles fonts, kerning, and linespacing quite well. I also find its built-in PDF conversion options a real bonus since it has lots of output options. This is especially important for POD distributors (like Ingram) that only accept pdf files for cover art.
Like any fairly robust software, there’s a bit of a learning curve. I have not explored all of the features in Scribus, but for me it really gets the job done. I should also mention that Scribus is Open Source Code, which means that it is constantly being scrutinized and upgraded.
Paint.net — Image Editing (http://www.getpaint.net/index.html)
This is somewhat easier-to-learn than GIMP, but with the plugins that you can get for Paint.net ( pronounced “paint dot net”), it handles most everything I throw at it. Layering, transparencies, color handling, editable text, blurs, smudges–the list goes on. I also like the fact that Paint.net has lots controls for layers, output, and canvas sizing. I’ve used it for everything from 50mg maps, book covers, web thumbnails, and a myriad of design projects. There’s even a PSD plugin that let’s you load Photoshop files, such as the templates that you can get from print shops and designers.
Sigil — Epub Editor (https://sigil-ebook.com/)
I use Sigil for creating epub files. Compared to Calibre, it has much less “overhead,” making it easier to use. There’s a preview pane, a contents pane, and a work pane that can be switched from a sort of WYSIWYG to code display (which I prefer). All of these panes are adjustable and can be undocked. Sigil really shines when performing search and replace work. It does have a built-in “preflight verifier” that is helpful (but it’s no substitute for EPUBCheck). With Sigil I’ve been able to create epub files for Kindle (KDP converts epub to mobi), Smashwords, and Xinxii, not to mention epubs for my own use.
BTW, Sigil is Open Source Code, too.
Crimson Editor — Source Code and HTML editor (http://www.crimsoneditor.com/)
VSDC Free Video Editor (http://www.videosoftdev.com/free-video-editor)
A powerful and robust video editor, this editor has loads of features. While the built-in “special effects” aren’t anything to write home about, it does let you create your own using transparencies, layering, and multiple embedded video files. VSDC has editable text graphics, audio controls, fading in/out, zoom, shift. It is non-linear, which means that you can put your elements (video, audio, images, etc.) almost anywhere within the editing file instead of in order from start-to-end.
VSDC has abundant conversion features that allow you to control the quality of the output, and a built-in previewer to “run” your video as you edit. It does lack some finer controls and functions, like switching back and forth from time location to frame location and certain zoom controls. However, it is the best free video editor that I’ve found.
Audacity — Audio Recorder and Editor (http://filehippo.com/download_audacity/)
Open Source Code! Free! Audacity is great for quickly editing and recording audio files. It can handle most of the file formats you’ll likely need (mp3, wav, oog, etc). Features include copy, paste, cut, audio fade-in/out, audio pitch control, special effects, noise reduction, multi-track mixing.
I use Audacity to edit sound files for both audio end-products and for use later on in video production.
VLC Media Player (http://www.videolan.org/vlc/index.html)
My go-to media player, VLC can handle most audio and video files. One of the things I like about it is the ability to speed up or slow down playback. I listen to and watch a lot of podcasts, but I prefer to download them while I’m doing something else and play them back at the max speed that I can understand. (Hey, I’m a busy guy!) VLC isn’t an editor, mind you, but it has some nice features, including the ability to convert file formats (mostly audio), playlist control, and a slew of available plugins.
VLC is also Open Source Code.