That bring-your-own-device movement drove Apple and IBM into each others arms last year in a partnership ballyhooed by IBM chief executive Ginni Rometty and her Apple counterpart Tim Cook to ensure a steady supply of business-focused apps for Apple gadgets.

Fast forward to Thursday when Apple (AAPL) made good on a promise to open-source its Swift programming language. This is geeky stuff, but for business customers this could lead to a groundswell of not just new iPhone apps and cloud services as well, said Phil Buckellew, IBM’s (IBM) vice president of enterprise mobile.

What many people forget is that as powerful as mobile devices are, much of their value comes from services that run elsewhere in someone else’s computer. In short, personal digital assistant Siri wouldn’t know much without her cloud.

“Right now, building mobile apps is the top pressing need for businesses of all sizes,” Buckellew told Fortune. “And to do that you need great developers, not just for the customer-facing applications, but for the cloud services as well. ”

For the past decade, software developers have shown a preference for open-source software—which they can download for free and use as they want to build products as long as they funnel key improvements or changes back into the code itself. One selling point of open-source, in addition to its negligible cost, is that many developers from many companies scrutinize the code and improve on it.

Proprietary software like Microsoft (MSFT) Windows and most Apple software, must be bought and paid for, and the source code is not readily available for tweaking and customization. Open source proponents view it as closed-off and restrictive. Until now, Apple was firmly in the proprietary software camp while IBM has been a huge proponent of open-source software including the Linux operating system, to Java development environments.

This decision by Apple to open-source Swift, announced at the Apple Worldwide Developer Conference in September, signals an important departure. Apple said Swift will code is available on the popular Github repository and will support applications for Linux and the various Mac operating systems iOS, OSX, watchOS and tvOS, according to the Apple release.

wift open source code is available via GitHub and includes support for all Apple software platforms — iOS, OS X®, watchOS and tvOS™ — as well as for Linux. Components available include the Swift compiler, debugger, standard library, foundation libraries, package manager and REPL

By virtue of the IBM’s deal with Apple, Big Blue developers have already used Swift to build hundreds of apps. Most of them prefer it to its precursor, a language called Objective C, Buckellew said.

“They don’t have to keep track of memory as they work,” he said. Plus, it’s great to be able to build programming logic that runs on the back-end servers or cloud, with the same language used on the front end. Developers can apply one set of skills to both sides of the application equation.

“Now that Swift is open sourced, the community can extend it to other top platforms including the back-end servers,” he said.

For more on Apple’s latest, check out this video.

For more from Barb, follow her on Twitter at @gigabarb, read her coverage at fortune.com/barb-darrow or subscribe via this RSS feed.

And please subscribe to Data Sheet, Fortune’s daily newsletter on the business of technology.

This story was updated at 7:00 p.m. EST with a link to Apple’s press release and more information about how Swift has been made available.