Subtitle Composer can be built/installed on all linux distributions and since recently windows support has been added to KDE Frameworks 5, so in theory it should be possible to compile it under windows too, instructions will be added as soon as it's been tried out.
Most linux distributions should already include subtitle composer. If you want to build latest version from git your self [instructions can be found here](https://github.com/maxrd2/subtitlecomposer/wiki/Building-from-sources)
Developers - if you would like to contribute some code please check [coding style doc](https://github.com/maxrd2/subtitlecomposer/wiki/Coding-Style).
Translators - if you would like to translate Subtitle Composer to your language please check [translation update instructions](https://github.com/maxrd2/subtitlecomposer/wiki/Updating-translations).