aegisub

advanced subtitle editor

Originally created as tool to make typesetting, particularly in anime fansubs, a less painful experience, Aegisub has grown into a fully fledged, highly customizable subtitle editor. It features a lot of convenient tools to help you with timing, typesetting, editing and translating subtitles, as well as a powerful scripting environment called Automation (originally mostly intended for creating karaoke effects, Automation can now be used much else, including creating macros and various other convenient tools).