Mordenkainen's Tome of Foes
Last night Nathan Stewart and Mike Mearls announced the next D&D manual on Fireside Chat. More will be revealed over the weekend what it will contain but as Mordenkainen is from Greyhawk it's a safe bet that it'll contain information about the multiverse and the different planes. We expect this to be released on 29th of May 2018.
So far we know that there will be a variant cover available, I'm a little underwhelmed by it but apparently the finished foil slip cover is much better.
Here's the announcement itself:
I'll keep updating this when we get anymore information but we are getting a full press release on Monday 5th.
UPDATE: 05/02/18
We now have an official product page.
Here's Mike Mearls giving an interview on the new release:
So this is going to be like Volo's Guide to Monsters, it'll contain lore about cosmic conflicts, information on the Gith and monsters.
The manual will be skewed towards higher level play with half of the entries having a Challenge Rating of 10 or higher. This is great because long running games were getting a little stale without homebrew material.
Here's everything you need to know about Mordenkainen from Chris Perkins himself!