Confluence means "a coming together" and has been helping workers do just that since 2004. Starting out as an enterprise wiki, it has evolved through the years into an all-round collaboration tool. Confluence is available as a SaaS or hosted product, powered by Java. It is the Atlassian product and it is designed to work with other Atlassian products.
Confluence has the widest spread application of Atlassian's products, it could be applied in almost any environment. It is free to open source institutions and non-profits. Pricing starts at just a charity donation of US$ 10 for hosted smaller installations for less than 10 users.