Wolfram|Alpha has relativity calculators. Solve problems related to relativistic kinetic energy, kinetic energy of a sphere, de Broglie relations, length contraction, aberration, redshift, Doppler shift, energy, momentum, time dilation or addition of velocities; the Bussard ramjet; gravitational redshift in a spherically symmetric spacetime; the Lorentz factor γ; the proper velocity formula; the rapidity formula; gravitational time dilation; and Doppler blueshift or redshift.
