To paraphrase Voltaire, if SME didn't exist, it would have to be invented. There are distributions such as ClarkConnect and IPCop whose functions overlap the SME Server's in various ways, and yes, you can take any flavor of Linux and make a server of it ... but there really isn't anything comparable to SME Server for ease of installation and simplicity of administration. File server, router/gateway and email server, running happily on very modest hardware -- a true boon for small businesses and organizations.