If you have the money there are excellent commercial packages available including PCI Geomatica, ENVI-SARScape, and Gamma. All of these provide powerful SAR processing solutions. However, if you want to save money there are Freeware alternatives. Here it is important to point out that there is a difference between Open Source and Freeware; the former freely distributes the source code while the latter is free to use but may not allow users access to the source code.