Concept and Prototype
In 1995, Toyota showed a prototype of the Prius. Here's a PDF. The body shape already resembles the first generation Prius, but the mechanical system is very different. The term "Hybrid Synergy Drive" did not exist yet. Instead Toyota called the hybrid system on this concept vehicle "Toyota EMS (Energy Management System)". The power-split-device and battery is nowhere to be seen. Instead the concept used a capacitor bank to store energy. The engine was mated to a continuously variable transmission (CVT) and motor. There has been speculation that Toyota deliberately did not show their Toyota Hybrid System (THS) as used in the first generation Prius for reasons of security. They most likely wanted to throw off their competitors, because at this time THS was already in development.
1995 Prius Prototype