Twist & Go, and a basic geared front hub motor that could be added to almost any bike - even a monkey could manage this. This simple lightweight setup is the oldest, and it is still around in various forms.
It also suffers from some major limitations:
Under powered - usually 15mph and much slower on the hills
Tired hands - twisting or pushing the throttle gets to be a pain.
Scooter-like - not really exercise oriented if you want a workout
Range (how far the ebike will go on a full charge)- limited, usually less than 20 miles. Efficiency with a throttle was not very good.
Batteries - lead acid & NiCd had low energy density, bad memory, and were bulky and heavy, struggling to deliver enough oomph.
Anxiety battery sizes tended to be smaller without a power meter to tell when you are going to run out of juice.
eBikes have evolved since the first iterations that were throttle only front drive motors. Some brands like GoCycle have innovated very capable eBikes using super advanced engineering.
These early designs are kind of like a "gateway drug" to more modern mid drive options that will retain their value for many years to come.