A lot of people are using this website, and it sounds intriguing, so I went to upload my DNA there. Now I would have felt fine doing this with an anonymous handle (DNA is medical information, after all), but the form to upload data requires my full name from AncestryDNA.

So, I then looked around for who GEDmatch is but can't find anything. Who are they?

Also, why can't I use their website anonymously?