IMVU is a graphical instant messaging client (3D chat) currently in beta stage with more than 3 million users.  The basic IMVU client is free.
The primary focus of IMVU is the ability to use personalized 3D avatars and environments that let the user interact with the person they’re chatting with. Full 3D scenes make users feel as if they are sitting with a friend in a coffee shop, on a Ferris wheel, etc. The secondary focus of IMVU is allowing the members to develop content that can be sold to other members for use in personalizing their avatars and environments.
Developed by Will Harvey, a video game developer and founder of There, a similar 3D virtual world, IMVU members also receive a personal homepage at no cost. Coding for IMVU homepages is similar to Myspace.
Unlike similar virtual worlds, IMVU contains its own economy with a credits-currency system. Partially based upon physical, real-world money, this economy funds the IMVU project. New members are given 1000 credits to purchase additional IMVU content, but beyond this initial gift, credits must be purchased via credit card, SMS, or money order.
The credits system in operation on IMVU allows members to access virtual items like fashion pieces (hair, clothes, skins, and accessories), pets, and 3D scenes. Each of these virtual items average $0.50 and are largely created by other members.