There are two kinds of fonts on Fontshare, Closed Source and Open Source.
The Closed Source are unique to Fontshare, designer, product and owned by ITF, and are therefore available nowhere else. While Open Source fonts are owned by their own designer, but are chosen by ITF for their quality before they resolve the technical problems related to the font (if there are problems) and then share them on their site.

Fontshare also offers pairs of fonts to try to guide you in your design choices.