Crowdin - Localize your product in a seamless way
Weblate - Weblate is a free web-based translation management system.
SDL TRADOS - Computer-Assisted Translation tool, enabling the use of Translation memory.
OmegaT - OmegaT is a free open-source translation memory application for professional translators written in Java.
POEditor - The translation and localization management platform that's easy to use *and* affordable!
Poedit - Poedit translations editor. The best way to translate apps and sites.