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