ffmpeg2dirac - fork of ffmpeg2theora, can enode into OGG Dirac but also Theora (obsolete)
VLC Media Player Can transcode from any source it supports into Ogg/Theora. WARNING: Apparently creates broken Ogg streams.
GStreamer GStreamer is a library that allows the construction of graphs of media-handling components, ranging from simple Vorbis playback to complex audio (mixing) and video (non-linear editing) processing.
Theorur is a GUI for Ogg/Theora streaming (Icecast2 system), written using gtk2.
Handbrake is a GUI/CLI free software for ripping/encoding DVD/Files into various containers and formats including theora & vorbis since September 2008.
firefogg is a Firefox extension that encodes locally and uploads in chunks or when encoding finishes
Video to Theora Simple and clear video (any format) converter to Theora (serves as a frontend to ffmpeg2theora), Released at FEB 2013.
Theora Converter .NET Batch converts almost any video file to OGG (.ogv) Theora format. This application is a graphical user interface for ffmpeg2theora 0.27. A GUI that supports 2 pass video encoding with Theora 1.1.1 (Thusnelda).