Unit Converter is an offline unit converter app for converting units. It has a lot of units you need to convert: acceleration, area, charge, mass, distance, energy, force, temperature, time, pressure, speed, viscosity, volume, and volume flow. Units can be converted to any unit in the app, and units from a lot of categories: mass, speed, power, energy, time, temperature, pressure, distance, and area. The converter also has a time converter.

It does have some quirks that have been discovered, but they don't appear to affect the functionality of the app.