Microsoft has announced its intention to "sunset" Project Spark, a horrible corporate buzzword that means "we're shutting it down". Project Spark was its user-friendly, 3D, game-development tool, which most famously gave the world some new Conker levels, and that launched with a costly pricing model. A change to that pricing model—and the appearance of a certain foul-mouthed squirrel—weren't enough to make Project Spark a hit, and so it "transitioned away from active development" last autumn.
Now, it's being shut down entirely. As of...now, you won't be able to find Project Spark on either the Windows Store or the Xbox Marketplace, while current users only have until December 8 2016 to make final preparations before Microsoft flips the big 'off' switch. I imagine this will be particularly crushing to people that spent a lot of time making games for the platform, and while it sounds as if you'll be able to continue developing and playing them offline, you won't be able to do much with your creations.
On a happier note, Microsoft says there have been no layoffs as the result of Project Spark's closure, as "many of our team members moved to other projects within Microsoft Studios" when it stopped being actively developed last year.
There's the possibility of a refund, in Xbox/Windows Store credits, if you purchased the Project Spark Starter Kit from a shop after October 5 2015. You can read more about that here.