Microsoft's latest move in its war on Apple's App Store rules is a list of 10 principles outlining what the Redmond company will and won't do to developers who publish apps for Windows 10 and distribute them on the Microsoft Store.
Microsoft says it will not block competing app stores on Windows and will not block apps because of a developer's business model, such as whether an app's content is installed on a device or streamed from the cloud.
Microsoft published the 10 principles a day after Congress released a damning report into anticompetitive practices at Amazon, Apple, Facebook and Google. The EU opened its investigation into Apple's App Store rules this June.
SEE: Top 10 iPad tips (free PDF) (TechRepublic)
"Apple's monopoly power over software distribution to iOS devices has resulted in harms to competitors and competition, reducing quality and innovation among app developers, and increasing prices and reducing choices for consumers," the US House Judiciary Antitrust Subcommittee wrote.
Setting out the new principles, Microsoft vice president and deputy general counsel Rima Alaily acknowledged the importance of app stores to software developers.
"We and others have raised questions and, at times, expressed concerns about app stores on other digital platforms. However, we recognize that we should practice what we preach," she said.
Microsoft's second principle regarding content streaming is central to its complaints about Apple's rules for Microsoft's Xbox xCloud game-streaming service.
After banning streaming games, Apple last month tweaked its App Store rules to allow services such as Sony PlayStation, Google Stadia, and Nvidia GeForce Now. But Apple is requiring these services to submit an app for each game rather than only vetting the game-streaming service app. Microsoft has objected to that rule.
Microsoft also says it will "not block an app from Windows based on a developer's choice of which payment system to use for processing purchases made in its app".
Google is stepping up its enforcement of a Play Store policy requiring companies that sell digital goods, such as content subscriptions, to use its billing system. Google is giving companies like Netflix and Spotify until September 31, 2021 to switch to its in-app billing system but will also apply the same rules to its own apps.
While Google Android allows users to install apps from third-party app stores, iOS users don't have that choice. The highest profile fight over in-app payments is between Apple and Epic Games, which rolled out its own in-app payment system for Fortnite.
Microsoft also "will not force a developer to sell within its app anything it doesn't want to sell".
This point touches on some of the complaints that iOS developers told members of Congress for its report into whether Amazon, Apple, Facebook and Google are violating antitrust law.
Andy Yen, CEO of encrypted email service ProtonMail, told The Verge that in 2018 Apple "out of the blue" demanded ProtonMail add an in-app purchase option to stay in the App Store.
According to Yen, Apple discovered that ProtonMail offered paid plans on its own website and then demanded it implement in-app purchases. ProtonMail had not created its own in-app payment system as Epic had done for Fortnite. Apple also prevented ProtonMail from updating its app until it complied, he said.
"There's nothing you can say to that. They are judge, jury, and executioner on their platform, and you can take it or leave it," said Yen.
"You can't get any sort of fair hearing to determine whether it's justifiable or not justifiable, anything they say goes. We simply complied to save our business."
ProtonMail's case is similar to Apple's recent demand that WordPress implement in-app purchases to sell domains or be blocked from updating its app. Apple eventually backed down from its demand, admitting it was wrong.
Microsoft vows not to prevent developers from communicating directly with their users through the app for legitimate business purposes, to apply the same standards to its own apps as competing apps, and to be transparent about its policies.
Microsoft's 10 principles build on ideas from the recently launched Coalition for App Fairness, whose founding members include Epic Games, Spotify, ProtonMail, Tile, and Basecamp, the maker of the Hey email app. Basecamp got into a fight with Apple after it was blocked from updating its app until it added in-app purchases.
However, Microsoft won't be applying the same principles to the Xbox store.
"Game consoles are specialized devices optimized for a particular use. Though well-loved by their fans, they are vastly outnumbered in the marketplace by PCs and phones," said Microsoft's Alaily.
"And the business model for game consoles is very different to the ecosystem around PCs or phones. Console makers such as Microsoft invest significantly in developing dedicated console hardware but sell them below cost or at very low margins to create a market that game developers and publishers can benefit from."