ClearOS (also known as the ClearOS System , formerly ClarkConnect ) is an operating system marketed by the software company ClearCenter. It is based on CentOS and Red Hat Enterprise Linux ,  designed for use in small and medium enterprises as a network gateway and network server with a web-based administration interface .  It is positioned as an alternative to Windows Small Business Server .  ClearOS succeeds ClarkConnect. The software is built by ClearFoundation , and support services can be purchased from ClearCenter .  ClearOS removes previous limitations to mail, DMZ , and MultiWAN functions.