One of the promises Wizards of the Coast made in the aftermath of the Open Gaming License 'crisis' back in January was that D&D Beyond would eventually have some kind of third party marketplace. Up until now, only official D&D books from WotC have been available there.
Now, however, there is a section of 'partnered content' -- six titles, including three Critical Role sourcebooks, as well as some older licensed items like the Rick & Morty boxed set and the Minecraft monster tie-in. The latter were already on DDB, but the 'Partnered Content' home for them is new, as is the Tal-'dorei Campaign Setting.
As of now you can pick up Explorer's Guide to Wildemount, Call of the Netherdeep, and the Tal'dorei Campaign Setting Reborn.
Tal’Dorei Campaign Setting Reborn
The definitive sourcebook for bringing the locations, people, creatures, and character options of Critical Role’s Tal’Dorei continent to ...
www.dndbeyond.com
While this 'partnered content' is a long way yet from the third-party marketplace mentioned earlier this year (which is likely a a couple of years away), it is notable that third party content is now appearing on the site.