What's the difference between VHCS, ispCP Omega and ispCP?

VHCS is a Virtual Hosting Control System which has not been updated for years

ispCP Omega (to simplify matters often called only ispCP) is a fork of VHCS to provide the much needed updates to VHCS and to continue development.

ispCP (without Omega) is a (planed) framework to support multiple servers. Do not expect it in the near future.