VIX allows you to automate virtual machine operations and is the engine behind for example VMware's vmrun command.
Supported on VMware Workstation 6.0.x and up, VMware Server 1.x and up, VMware ESX3.5U2+
Download. The link for the API page no longer offers a working download (strange)
This one however works, but you do need to login: VMware VIX 1.14 it is probably better to install VMware Workstation Professional which bundles VMware VIX.