Microsoft had previously taken a few steps to align itself more with open source communities, including joining the Linux Foundation, joining the License on Transfer Network, and joining the Red Hat-led GPL pledge (“We doubled down on this new approach when we stood with Red Hat and others to apply GPL v. 3 “cure” principles to GPL v. 2 code.”)
OIN is a patent pool relating to Linux — broadly defined to include many elements in the Linux stack.
Microsoft has historically been one of the few non-NPEs to exact patent royalties for Linux, and famously licenses patents for Android devices (which use the Linux kernel). The prior linked article explains some of the history of Microsoft’s enforcement efforts, which were focused in part on the FAT (File Allocation Table) patents. However, news reports have been unclear on the exact effect that joining OIN will have on Microsoft’s Android patent license program.