Having said that, one of our favourite tools is the open source CMS: Umbraco.
As well as being Registered Umbraco Partners, we created and maintain a few Umbraco packages. Several of our team are also Umbraco core contributors.
As well as being an outstanding CMS, the Umbraco international community is second to none. As a team we enjoy attending, sponsoring and speaking at Umbraco events and conferences. We also instigated and help run the Umbraco Mentoring program for both new and experienced developers and site builders.