Subordination is completely free and open, you can use it in any way you want. Feel free to contribute your code.
Although the primary focus is on translation, you can shift the timing of your subtitles, add new and edit existing entries.
The updates come automatically, so you can always have the latest version. The Windows version supports delta updates.
You can upload your translation directly to Opensubtitles.org. There are several requirements though.
Subordination automatically saves and restores your project in a state you left it in your previous session.
The application is avaliable in two flavours for OS X and Windows. Both versions are 64-bit and look slightly differently on each platform.
Subordination supports a lot of video formats and allows you to tie your subtitles to a video file. The video module loads separately with your persmission.
You can work on several projects simultaneously. Switch between them by a single click - they all are listed on the left panel.