Penguin Subtitle Player is especially useful for online video streaming websites that don't support subtitles or don't allow custom subtitles. You can also use Penguin Subtitle Player to display subtitles in a custom position, like on the black top/bottom bands, or to display multiple subtitles in the same time.

Penguin Subtitle Player is a simple open source Qt5 subtitle player which can be used to display subtitles on top of online video streaming websites that don't support subtitles or don't allow using custom subtitles. 

You can also use Penguin Subtitle Player to display subtitles on custom positions (like on the black bottom/top bands), or to display multiple subtitles in the same time (since the app can be launched multiple times), for video players or video streaming websites that don't support this by default.

Various video players like Totem or VLC (with the VLSub extension) already support downloading subtitles from OpenSubtitles based on the video name or hash, but Subliminal supports multiple subtitle websites: Addic7ed, BierDopje, OpenSubtitles, SubsWiki, Subtitulos, TheSubDB and TvSubtitles, so there are better chances for downloading working subtitles that match your video.

VLSub is a VLC extensions to search and download subtitles from opensubtitles.org. The extension can search either based on the video hash or its IMDB title.

The extension can download subtitles in about 49 languages, including English, Arabic, Bulgarian, Czech, Dutch, French, German, Greek, Hebrew, Hungarian, Indonesian, Italian, Japanese, Polish, Portuguese, Romanian, Russian, Serbian, Spanish, Swedish, Turkish and more.

Subtitle Editor 0.36.1 was released today, the new version bringing mostly bugfixes:

Subtitle Editor is a GTK+2 tool to edit subtitles for GNU/Linux/*BSD. It can be used for new subtitles or as a tool to transform, edit, correct and refine existing subtitle. This program also shows sound waves, which makes it easier to synchronise subtitles to voices.

Subtitle Editor is a GTK+2 tool to edit subtitles for GNU / Linux / *BSD. It can be used for new subtitles or as a tool to transform, edit, correct and refine existing subtitle. This program also shows sound waves, which makes it easier to synchronise subtitles to voices. There are a lot of changes from version 0.30.0 which is in Ubuntu Karmic (by the way, even Lucid has version 0.30.0 and not 0.36.0) and the latest version. You can see all the changes and features @ Subtitle Editor homepage.