Renkoo, a Redwood City, Calif-based startup that is fast approaching its fourth birthday is rebooting…again. Co-founded by Adam Rifkin (CEO) and Joyce Park (CTO), the company had launched Renkoo.com as a social planner, pitching themselves as Evite 2.0. But in 2007, the pair changed tactics and started developing applications for social networks.

Renkoo built half a dozen apps — including Booze Mail for Facebook and MySpace — and got a lot of people (about 36 million) to use those apps, but it got bored because “these applications were not fulfilling to us because although they were entertaining, they did not help people help other people,” they write on their blog. With Facebook-app mania raging, the company was able to raise a whopping $6 million in a second round of funding in February 2008, bringing the total VC infusion to $9 million. Matrix Partners was one of its main investors.

Now it’s rebooting again. What is Renkoo 3.0? “We are currently working on a brand-new application that employs everything we’ve learned for the last four years — and enables a suite of voluntary actions that everyone can do in the United States and around the world,” they write on their blog. In other words, a social app for charitable causes, in the mold of Sean Parker’s Causes effort. How that translates into a business is anyone’s guess.

Update: Team Renkoo thinks the cynical-me needs to develop a heart and do good and not worry about business models. Just a difference of opinion I guess!