After two years since the previous version, a new YouTube-DL GUI (YouTube-DLG) version was made available for download recently. The new 0.4 version ships with a a new user interface, easier format and save path selection and more.

YouTube-DL GUI is, like its name suggests, a graphical user interface for the powerful command line tool youtube-dl, available for Linux and Windows. In case you're not familiar with youtube-dl, this is a popular tool that allows downloading videos from YouTube and around 1000 other websites.

Shotcut is a free, open source Qt5 video editor developed on the MLT Multimedia Framework (it's developed by the same author as MLT), available for Linux, Windows and Mac. Under the hood, Shotcut uses FFmpeg, so it supports many audio, video and image formats, along with screen, webcam and audio capture.

Penguin Subtitle Player is especially useful for online video streaming websites that don't support subtitles or don't allow custom subtitles. You can also use Penguin Subtitle Player to display subtitles in a custom position, like on the black top/bottom bands, or to display multiple subtitles in the same time.

If you find video editors to be confusing and all you need is to just cut a portion of a video, you can try LosslessCut, an application available for Linux, Windows and Mac.

LosslessCut was especially created to make it easy to quickly extract parts of video files from a video camera, GoPro, drone, and so on, without losing video quality.

Stream2Chromecast is a command line Chromecast media streamer for Linux. The tool can transcode unsupported formats in real time and play them on the Chromecast.

The original Screenkey was abandoned but thanks to Yuri D'Elia, the application lives on, through a fork that's an almost complete rewrite of screenkey 0.2 (the last version released by the original developer), which includes quite a few improvements and new features, such as:

Penguin Subtitle Player is a simple open source Qt5 subtitle player which can be used to display subtitles on top of online video streaming websites that don't support subtitles or don't allow using custom subtitles. 

You can also use Penguin Subtitle Player to display subtitles on custom positions (like on the black bottom/top bands), or to display multiple subtitles in the same time (since the app can be launched multiple times), for video players or video streaming websites that don't support this by default.

OBS Studio is a free, open source application which allows video recording and live streaming. The app can be used to stream to various popular websites such as Twitch.tv, YouTube, Hitbox.tv, Vaughn Live / iNSTAGIB.tv, DailyMotion, Connectcast.tv, GoodGame.ru, CyberGame.tv, CashPlay.tv along with custom streaming servers.

The original Open Broadcaster Software was rewritten, with the main goal of being multiplatform, along with a more powerful API and a more thorough feature set. The new multiplatform OBS Studio is currently in alpha and is available for Linux, Mac OS X and Windows.

HandBrake is a popular free and open source video transcoder available for Linux, Windows and Mac OS X. The tool works great however, the app widgets are black under Unity, this issue being caused by Ubuntu's overlay scrollbars:

By default, mps-youtube is basically a YouTube audio player (and downloader), but you can enable external video playback (via mpv or MPlayer) from its options:

HandBrake, a free, open source video transcoder for Linux, Windows and Mac OS X, has been updated to version 0.10.0, getting support for new encoders, like H.265 and VP8, along other interesting changes.

VLC is a great media player but it lacks a minor, yet pretty important feature, some would say: an option to resume playback from where you left off.

The tool comes with basically all the features you need in a screencast app: record the entire screen (with multi-monitor support), record a fixed rectangle, follow the cursor, record OpenGL applications (which can be used to record games), record audio input (PulseAudio, JACK and ALSA), options to scale the video, to record (or not) the cursor, to pause/resume the recording and so on. It even has experimental live streaming support.

YouTube uses Dynamic Adaptive Streaming over HTTP (DASH) for delivering videos and along with that, it serves the audio and video in two separate streams for some resolutions/formats. For instance, resolutions like 1080p and 480p are available only with separate audio and video streams.

youtube-dl, a popular command line tool for downloading videos from YouTube and other similar websites, was updated recently with proper support for DASH and separate audio and video streams: the tool can now automatically combine / merge / multiplex the audio and video formats offered by YouTube.