Social software enables people to rendezvous, connect or collaborate through computer-mediated communication and to form online communities. Broadly conceived, this term could encompass older media such as mailing lists and Usenet, but some would restrict its meaning to more recent software genres such as blogs and wikis. Others suggest that the term social software is best used not to refer to a single type of software, but rather to the use of two or more modes of computer-mediated communication to engage in community formation. In this view, people form online communities by combining one-to-one (e.g., email and instant messaging), one-to-many (Web pages and blogs), and many-to-many (wikis) communication modes. In many online communities, real life meetings become part of the communication repertoire. The more specific term collaborative software applies to cooperative work systems.
Also see my del.icio.us links here. In particular, please do take a look at the Free/Libre and Open Source Software links in education and others related to FLOSS.