Co-founded in 2004 by Eric Ries (the author of The Lean Startup and creator of the concept), IMVU was one of the first successful lean startups. It is a large virtual 3D chat environment where you can dress up an avatar, create a home page for it, and talk with new people online. The original product the company made did not contain these features, however. The product evolved through the lean startup process to become what it is today.
Starting from Scratch
According to this lecture from the founders, the company did not initially know what features their product would have or who their customers would be. They started with a basic chat add-on, and through testing and talking with users, they discovered what features were in most demand.
Continuous customer interaction was essential as they developed the product. They discovered not only who would be interested in it, but also how to make it more attractive to a larger audience. The product improved through the process of getting a lot of customer feedback and doing rigorous testing.
Additionally, Agile Development optimized the process of building the product. They deployed the minimum viable version of each new feature during iterations and did continuous integration and deployment. The business evaluated new features rapidly and either discarded or improved them.
The use of "Commoditized Technology" including open-source software was essential for success as well. This keeps costs low for a startup while allowing for greater customization and flexibility to meet the needs of the project.