Modulation diodes usually refer to diodes specifically designed for ring modulation.
Varactor diodes are small power diodes used for automatic frequency control (AFC) and tuning
Zener diode is a product that replaces Zener electronic diode.
Avalanche diode is a transistor that can generate high-frequency oscillations under the action of an applied voltage
A fast turn off (step recovery) diode is also a type of diode with a PN junction
Double base diode (single junction transistor) is a three terminal negative resistance device with two bases and one emitter,
