VVT : (Generic) Vairable Valve Timing, each company has a different way of doing it but all are looking for the same result, better performance.
VTEC : Uses 2 cam profiles, one for low RPM one for high RPM. Meaning the lift, Duration, valve timing a ALL Change.
i-VTEC : Changes the timing while on each cam profile, making the change from low RPM to high RPM smoother.
MIVEC : Changes lift, duration, and valve timing similar to VTEC, using 2 different cam profiles.
Toyota VVT-i : changes intake timing in relation to the exhaust cam
Toyota VVTL-i : adds another cam profile so it can change like VTEC & MIVEC for high RPM's
VANOS : Changes only the intake valve timing, it is continuous unlike [most] VVT systems
Double VANOS : Changes both intake & exhaust timing
The Variable Timing in the Ecotec (DCVCP) changes the valve timing in relation to RPM it does NOT change the lift or duration. Making it closest to double VANOS