Simple unit converter that includes a wide array of types

Acceleration
Angle
Angle velocity/frequency
Area/2D
Concentration mass
Dispersion
Duration/time
Electric charge
Electric current
Electric potential difference/electricity
Electric resistance/electricity
Energy/work
Force
Frequency
Fuel efficiency
Illuminance/light
Information storage/data
Length/distance/height/altitude
Mass/weight
Power/electricity
Pressure/stress/strength
Speed/velocity
Temperature
Torque
Volume/3D

Let us know if there is anything to add.