[ excerpt with some modifications from author's website ]

GTKsubtitler is a small program for editing and converting subtitles.

o It supports: moving, merging and converting to iso-8859-1 and
  iso-8859-2

o Four subtitle formats: Time, MicroDVD, Subviewer and SubRip

WWW: http://www.gtksubtitler.prv.pl/