VMware PowerCLI is one of the most successful command line tools for managing your VMware products. With the many existing cmdlets designed for the system administrator or vSphere Admin, PowerCLI is the easiest and most powerful tool for managing your environment.
PowerCLI Extensions gives PowerCLI users access to early access functionality by extending the core PowerCLI cmdlets to include new experimental features and gives PowerCLI customers the ability to provide early feedback.
Also read the following article by Brian Graf: VMware Instant Clone is now at your fingertips with the updated PowerCLI Extensions fling!