A trademark filing in the EU has unveiled an unannounced Bungie project: "Matter." Submitted by a UK law firm representing the US company, Matter is submitted under the ratings for "video game software" and "electronic game services provided through the internet or other communications network."
In other words, it is a video game. Will it be a PC game? Hopefully. It is probably worth noting that the second rating may also indicate a service that allows downloading or playing games, which is unlikely when Bungie launches its own Steam competitor or eSports tournament service.
The only other thing of note is the image that accompanies the submission, probably the tentative service or game logo, which looks as if someone put some words in front of a bunch of exploding cans of the spray paint.
Thanks to the posters with eagle eyes Resetera to find the archiving.