I think the list should either be kept out of the article altogether, or it should be explicitly limited to a small number (say half a dozen) of particularly notable clustering systems, for which some strong argument can be made for their inclusion beyond "it's a clustering system" or even "it's a free clustering system". By a strong argument, I mean statements such as "it's the most widely used free clustering system for Linux" or the like. Anything less restrictive is just an invitation for an unencyclopedic link farm. —