Fatorials are very useful in several fields: the factorial operation is encountered in many different areas of mathematics, notably in combinatorics, algebra and mathematical analysis. This application allows to calculate very big fatorials - for those who like big numbers. For example, try calculate 150!
You will get:

57133839564458545904789328652610540031895535786011264182548375833179829124845398393126
57448867531114537710787874685420416266625019868450446635594919592206657494259209573577
89293253572904449624724054167907221184454371222696755200000000000000000000000000000000
00000