VIX
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+
VMware VIX 1.1 API reference Guide
VMware VIX 1.6 API reference Guide
vmrun commands (see also VIX API link above)
Whitepaper: Migrating From VIX API to the vSphere Guest Operations API
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.
Presentations
VIX API Tech Talk Partner Exchange
