Talk about your kumbaya moment. Microsoft, the company that is the arguably the standard bearer for proprietary or closed-source software, has joined the Eclipse Foundation, a group dedicated to promoting the use and growth of open-source software.

Microsoft msft announced the news in a blog post on Tuesday, the day after it shook things up by saying that its Windows-focused SQL Server database would be coming, at least in part, to Linux.

IBM ibm started the Eclipse Project in 2001 to build an integrated development environment for Java applications. An IDE basically gives the developer an easier way to start programming and cut time to market. Java was (and is) a popular programming language for building business applications.

And, as IDC analyst Al Hilwa pointed out by email, Eclipse was an attempt by rivals to counter Microsoft’s own Visual Studio IDE push. Three years later IBM turned the Eclipse effort over to a multi-vendor foundation.

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Foundation members up till now included IBM, SAP sap , Google goog , Red Hat rht , Novell, CA, and Oracle orcl . They are basically all the major software players with the notable exceptions of Microsoft and Amazon Web Services. Now strike Microsoft off that hold-out list.

Read Fortune’s Q&A with Microsoft CEO Satya Nadella

To be fair, Microsoft started making nice to the open source crowd a couple of years ago after it realized that many of the newest cloud-oriented workloads relied on open source software including the Linux operating system.

Big cloud players like Google goog and Amazon amzn were not using Microsoft’s commercial software to build their infrastructure. And, perhaps just as worrisome to Microsoft, was that many programmers coming out of school also preferred free (or cheap) open source tools, languages, and other software over Microsoft’s own Visual Studio-Windows-Office trifecta.

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As Microsoft started to build Azure as a competitive response to Amazon Web Services, it started to make moves to woo or at least be nice to the open source constituency. That started under then-chief executive Steve Ballmer but has accelerated under his successor Satya Nadella.

Still for those of us around for a lot of the verbal sparring a decade ago, these announcements remain jarring.