Unitless is a lightweight alternative to the various unit libraries that create quantities with units (hence the name). Instead, it provides a system for doing unit conversions which is easy-to-use and readable. The system is written in cython so that it can be used in high-speed numerical codes without any loss of speed, yet still available in python scripts and the interpreter. Usability is important so that Unitless can be used for both numerical codes and the analysis of their outputs.
It is in an early stage of development, but the intended functionality looks something like:
import unitless
u = unitless.Unit_System('CGS')
print u.meters_per_second
print u.exajoules_per_gigayear
print u.pounds_per_centimeter_second2