Lokalize - Lokalize is a computer-aided translation (CAT) system that focuses on productivity and performance.
Gorm - Gorm .po file editor
POEditor - The translation and localization management platform that's easy to use *and* affordable!
Crowdin - Localize your product in a seamless way
OmegaT - OmegaT is a free open-source translation memory application for professional translators written in Java.
Better PO Editor - Better PO Editor is an editor for .po files, used to generate compiled gettext .