PMLink is a Social Community for all Project, Program, and Portfolio Managers out there willing to discuss best practices, methodology, tools and share general content in the field of Project Management.
ERP Community is a Social Networking site for ERP professionals, user and enthusiasts.
Green Project Managers is the largest group of Green Project Managers on the Planet, with more than 12k members on Linkedin. Green Project Managers has recently launched a Social Networking site to help leverage collaboration across Green PMs around the world.
SAP Community is the largest non-official SAP group on Planet, with more than 260k members on Linkedin.