Procempa, Porto Alegre, RS, Brazil
Procempa has about 400 virtual machines running various versions of Debian to support applications and services for the city of Porto Alegre, whose use spans more than 15 years. We use Debian for running DNS, e-mail, web servers, Java application servers, and network shares (Samba), amongst other services.
We chose Debian due to its overall quality, best in industry package management and commitment to Free Software.