Jubler is a free and open-source subtitle editor. The tool can be used to author new subtitles, or to edit existing text-based subtitles. In doing so, Jubler allows users to include additional information in the subtitles of video broadcasts. At the same time, the tool also enables the translation of videos into different languages.

Jubler is available for use on Linux, Windows XP, and Mac OS X.

http://www.jubler.org/