Social Source Commons

POEditor is an online localization tool that provides a very simple user interface and many helpful features for developers and translators.
It works with many file types such as .po, .pot, .strings, .xml, .resx, .xsls, which you can use to manage your translation projects.
Features such as the POEditor translation memory or its reference language option make it one of the best options for software translation.
It is free for open source projects and limited for others.