The École Polytechnique Fédérale de Lausanne is developing a Web 2.0 social software called eLogbook and designed for sustaining interaction, collaboration, and learning in online communities. This chapter describes the 3A model on which eLogbook is based as well as the main services that the latter provides. The proposed social software has several innovative features that distinguish it from other classical online collaboration solutions. It offers a high-level of flexibility and adaptability so that it can fulfill the requirements of various Communities of Practice. It also provides community members with ubiquitous access and awareness through its different interfaces. Finally, eLogbook strengthens usability and acceptability thanks to its personalization and contextualization mechanisms.