The case you're referring to was the adoption of a Linux based OS (LiMux) by the city administration of Munich - here is the Wikipedia article on the subject.

Unfortunately, Munich totally rolled back Linux adoption for some shady reasons later on:

Microsoft had announced in 2013 its willingness to move its German headquarters to Munich in 2016, which according to Reiter though, is unrelated to the criticism they've presented against the LiMux project.