It's an abrupt setback to Microsoft's effort to juice up its struggling mobile platform by building various "Windows Bridges."
The idea was to make it easy for developers to bring their wares into the Microsoft Windows Store app market, helping alleviate its poor selection compared to the Android and iPhone app stores.
The other two Windows Bridges, Project Centennial (for old-school Windows software) and Project Islandwood (for bringing over iPhone apps), will proceed as planned, the company said in a blog post on Thursday .
Reading between the lines, it sounds like the lion's share of developers interested in the Windows Bridges are at least partially working on iPhone apps already.
For those few Android-only developers, Microsoft recommends looking into Xamarin - the startup Microsoft bought yesterday for a reported $500 million, which lets developers write a bit of code once and run it anywhere.
News of Project Astoria's shutdown doesn't come as much of a surprise: In November, reports emerged that Project Astoria was on indefinite hiatus, as its work-in-progress website was unexpectedly taken down.
Other bridges to cross
Basically, Microsoft says in that blog entry, the developers for whom Project Astoria was intended found it to be an unnecessary addition to the Project Islandwood tool for iPhone apps.
"We have carefully considered this feedback and decided that we would focus our efforts on the Windows Bridge for iOS and make it the single Bridge option for bringing mobile code to all Windows 10 devices, including Xbox and PCs," Microsoft writes in that blog entry.
Right now, Microsoft writes, Islandwood is best-suited for bringing iPhone games to Windows 10, with stuff like robust graphics support. The new focus, with the demise of Project Astoria, is to expand it and make it better for bringing all kinds of iPhone apps over.
Ultimately, the real story here is that while Microsoft may have given up on Project Astoria, it's still working really hard to bring as many games, apps, and tools to the Windows Store as it possibly can, as it works to bolster Windows 10 and get more people to adopt the new operating system.