Aegisub

Aegisub () is a free open-source cross-platform subtitle editing program. It is used professionally by companies like Crunchyroll and extensively in fansubbing, the practice of creating or translating unofficial subtitles for visual media by fans. It is the successor of the original SubStation Alpha and Sabbu.
It has been designed for timing and styling of subtitles, as well as the creation of karaoke. Aegisub's native subtitle format is Advanced SubStation Alpha text, which supports subtitle positioning and styling. The program also supports other common formats such as SubRip. Features include support for timing to both audio and video, and allows for many video processing bindings to process those, such as FFmpeg and Avisynth. It can also be extended with the Lua and MoonScript scripting languages.
In fansubbing terms, Aegisub is used for translating, timing, editing, typesetting, quality checking, karaoke timing and karaoke effecting. Although, many groups use different tools for some of those steps, such as Adobe After Effects for typesetting, or a simple text editor for translation.