Fashion Project is a new-ish online secondhand clothing retailer with one important difference from other companies in its market: 55% of proceeds go to charity.
The company focuses on well known, mid to high end designers and the site is distinctively modern, with clean lines and minimal use of color. It's a cool place to be. From a quick sampling of items within several categories, clothing is priced in about the same range as Thredup's higher end pieces (but noticeably lower on designer shoes), but the site layout and product images and descriptions are considerably better.
I don't tend to buy much from Fashion Project's preferred brands (Trina Turk, Elie Tahari, Anne Fontaine), so I don't really know where to start, but I think they're capable of appealing to a unique niche within the secondhand market, and that's a great thing. The more the merrier.