MKVToolNix
MKVToolNix is a free and open source, multi-platform, universal and powerful set of tools for working with MKV format files
Avidemux
Avidemux is a free and open source, multi-platform video editor designed for simple tasks: cutting, filtering and encoding
VideoMorph
VideoMorph is a free and open source, multi-platform program for converting videos to various formats
Ciano
Ciano is a free and open source simple multimedia converter for Linux
MystiQ
MystiQ is a free and open source powerful audio and video converter, graphical interface for FFmpeg
Curlew
Curlew is a free and open source easy-to-use audio and video converter for Linux
traGtor
traGtor – free and open source audio and video file converter, GUI for FFmpeg
Shutter Encoder
Shutter Encoder is a free and open source video converter, image and audio handles tool
Selene
Selene – free and open source audio/video converter for converting files to various formats
HandBrake
HandBrake – free and open source multiplatform, multithreaded transcoder converting video from nearly any format to a selection of modern, widely supported codecs