Great Downloader easy to use can convert into multiple file formats. Fast and impressive
GTK YouTube Viewer - A lightweight application for searching and streaming videos from YouTube.
Video DownloadHelper - Browser extension to download videos from the Web
FreeTube - FreeTube is an open source desktop YouTube player built with privacy in mind.
youtube-dl-gui - A cross platform front-end GUI of the popular youtube-dl written in wxPython.
Minitube - Minitube is a YouTube desktop application.
Youtube Video and Audio Downloader - Download YouTube videos in all available formats and extract the original audio files.