umbraco is an open source project with roots back to year 2000 even though it wasn't released as open source until 2004. Prior to that it was founder Niels Hartvig's home-grown weapon of choise for working as a freelancer.
Today it has grown to be among the top fifteen most popular open source .NET applications and in May 2008 we hit a milestone at 50.000 installed and active websites (double up from 25.000 in April 2007).
umbraco is a registered trademark of Niels Hartvig