If you are looking for a multi-platform text-based subtitle editorsthen you can try Jubler. Jubler is written in java it can be used on any machine that has got the Java Runtime Environment(JRE). So you can use this as a subtitle editor for MAC, Linux and Windows. You can use Jubler as an authoring software to create new subtitles or as a tool to convert, correct, transform and refine existing subtitles.

You can use Jubler to edit text based subtitles very easily. It supports most popular subtitle formats like Advanced SubStation, SubStation Alpha, SubRipl SubViewer (1 and 2), MicroDVD, MPL2 and Spruce DVD Maestro. You can even extend it to support other file types also. The main features include subtitles preview in realtime or in design time, spell checking, translation mode and styles editing.