Convert thousands of units, even calendars, with NumericalChameleon
NumericalChameleon is a free software that will let you convert numbers with a precision of up to 1000 significant figures.
It supports more than 3200 units in 82 categories, including not only all important physical units of categories like length, area, volume, electricity, magnetism, force, power, energy, pressure, mass, temperature, velocity, acceleration, radioactivity and time, but also exchange rates, timezones, spoken numbers (literally and by audio*), roman numbers, 35 radices, bits & bytes, screen resolutions, color codes, uni-codes, international dial codes, calendar and holiday calculations, phonetic alphabets and more.
The graphical user interface is pleasant and efficient. The user has unlimited access on all categories, units, icons, filters and themes, being also able to add, modify, hide or delete them.
All configuration data are stored in flat files. You need the Java Environment in order to use this program.