I think Pork Pie has somewhat oversold Cremona. Classically, it is a graphical technique to determine the loads in the members of a planar truss taking into account the applied loads and locations, the reaction loads and locations, and the geometry of the (proposed) truss design. It is basically static analysis of the framework. Once the member loads are determined, that information can be used to size the members for their appropriate tension or compression capacity.
In the U.S. this is normally simply termed static analysis. However, it may be that in Europe the Cremona name is used more popularly due to its origination in Italy.
In this day and age, manual analysis of this sort, which is laborious, has been supplanted by Finite Element Analysis programs which, for spaceframes, is an automated version of the same technique but also is more advanced in that it takes into account the elasticity and deflections of the members. (Which can also be done manually, but is REALLY laborious, iterative, and open to human error.)