AegiSub is a free, open code subtitle editor, specifically designed to work with SSA and ASS formats.
The program tries to work helping in all processes working on subtitles, editing, image synchronizing, etc. AegiSub increases and improves the functions you can find in other similar programs.
AegiSub includes many specialized utilities to complement its generic interface (which is clear and managable), making it one of the most advanced SSA/ASS subtitle editors on the market. Its complete help manual, with step by step tutorials, will guarantee your work is as effective as possible right from the start.