Multimedia Toolbox

Blender is the free and open-source 3D creation suite. It supports the entirety of the 3D pipeline—modeling, rigging, animation, simulation, rendering, compositing, video editing, and motion tracking.

Audacity is free, open source software for recording and editing sounds. You can use Audacity to record live audio, convert tapes and records, edit sound files, change the speed or pitch of a recording and much more.

VLC is a free and open source cross-platform multimedia player and framework. Owned by the non-profit organization VideoLAN.

MPV is an audio and movie player based on MPlayer and mplayer2. It supports a wide variety of video file formats, audio and video codecs, and subtitle types. It shares some features with the former projects while introducing many more.

• Streamlined CLI options
  MPlayer's options parser was improved to behave more like other CLI programs, and many option names and semantics were reworked to make them more intuitive and memorable.
• On Screen Controller
  While mpv has no official GUI, it has a small controller that is triggered by mouse movement.
• High quality video output
  mpv has an OpenGL based video output that is capable of many features loved by videophiles, such as video scaling with popular high quality algorithms, color management, frame timing, interpolation, and more.
• GPU video decoding
  mpv leverages the FFmpeg hwaccel APIs to support VDPAU, VAAPI, DXVA2, VDA and VideoToolbox video decoding acceleration.
• Embeddable
  A straightforward C API was designed from the ground up to make mpv usable as a library and facilitate easy integration into other applications.

Rhythmbox is an audio player for Linux that plays and organizes digital music. Inspired by Apple's iTunes, it is free software that is designed to work well under the GNOME Desktop using the GStreamer media framework.

Among the many features of Rhythmbox, you will find:

Easy to use music browser
Searching and sorting
Comprehensive audio format support through GStreamer
Internet Radio support including last.fm streams
Playlists
Display audio visualizations
Transfer music to and from iPod, MTP, and USB Mass Storage music players
Display album art and song lyrics downloaded from the internet
Play, rip, and burn audio CDs
Automatically download audio podcasts (also from iTunes)
Browse, preview, and download albums from Magnatune and Jamendo

Inkscape is a professional vector graphics editor for Linux, Windows and macOS. It's free and open source.

I use it to get the contents of my (legally owned) DVDs/BDs onto my PC for further processing (in MKVToolnix, Handbrake). I love that it's pretty much a one click operation to get all content including subtitles, alternative audio tracks etc. off the physical media.

ImageMagick is a software suite to create, edit, and compose bitmap images. It can read, convert and write images in a variety of formats (about 100) including GIF, JPEG, JPEG-2000, PNG, PDF, PhotoCD, TIFF, and DPX. Use ImageMagick to translate, flip, mirror, rotate, scale, shear and transform images, adjust image colors, apply various special effects, or draw text, lines, polygons, ellipses and Bézier curves. ImageMagick is free software delivered as a ready-to-run binary distribution or as source code that you can freely use, copy, modify, and distribute. Its license is compatible with the GPL. It runs on all major operating systems. The functionality of ImageMagick is typically utilized from the command line or you can use the features from programs written in your favorite programming language. Choose from these interfaces: MagickCore (C), MagickWand (C), ChMagick (Ch), Magick++ (C++), JMagick (Java), L-Magick (Lisp), PascalMagick (Pascal), PerlMagick (Perl), MagickWand for PHP (PHP), PythonMagick (Python), RMagick (Ruby), or TclMagick (Tcl/TK). With a language interface, use ImageMagick to modify or create images automagically and dynamically.

My main use cases: Adjusting track titles after ripping DVDs; transferring Opus audio tracks from YT-Downloads into standalone MKA audio files; remuxing movies from legacy container formats (avi, flv, ...)

fre:ac is a free audio converter and CD ripper with support for various formats and codecs. It will convert between MP3, MP4/M4A, FLAC, Vorbis, Opus, AAC, WAV, WMA and other formats.

With fre:ac you easily rip your audio CDs to FLAC or MP3 files for use with your mobile player or convert files that do not play with other audio software. You can even convert whole music libraries retaining the folder and filename structure.

The integrated CD ripper supports the freedb online CD database. It will automatically query song information and write it to ID3v2 or other title information tags.

Portable version: https://portableapps.com/apps/music_video/freac_portable

Free and simple video editor that supports a variety of file types and automated tasks.

Professional digital photo management software to organize, tag, compare and process photo collections.

GIMP is a free program for such photo retouching, image composition and image authoring. Essentially it's the closest thing to Photoshop you can get for free.

Convert videos to formats that work on your mobile phone, tablet, TV media player, game console, computer, or web browser.