Amara - Amara
Poedit - Poedit translations editor. The best way to translate apps and sites.
dotSUB - The leading way to caption and translate videos online
POEditor - The translation and localization management platform that's easy to use *and* affordable!
PO File Editor - A FREE online editor that helps you manage translations in PO files for your multilingual software projects.
translated.by - It's called collaborative translation.