Alternatives to Trello - https://opensource.com/alternatives/trello
4 Google Apps Projects Mangers should consider - http://www.techrepublic.com/blog/google-in-the-enterprise/four-google-apps-project-managers-should-consider/
The Best 7 Tools and Services for Project Management - http://www.itproportal.com/2013/06/13/the-best-7-tools-and-services-for-project-management/
Reviews
Review of Do.com Social Productivity Tool - http://www.brighthubpm.com/software-reviews-tips/127598-review-of-do-com-social-productivity-tool/