Field programmable gate arrays (FPGAs) are a special type of integrated circuit that consists of logic gates and memory blocks that can be configured with code to implement digital computations. Historically FPGAs could only process digital signals. These days however, FPGAs have evolved to also consist of data converters that can process analog signals.
FPGAs are a central part of a Software-defined Radio as they manage the real-time processing of digitized data. FPGAs vary in complexity and can cost from a few dollars to many thousands of dollars.
Over at Walk N’ Squak coding blog there’s a nice introduction to FPGA design for software engineers. While there are many FPGA development boards out there, the authors like the Tiny FPGA boards. This is a new series of low-cost, open-source FPGA boards in a tiny form factor. The Tiny FPGA lets you use an open-source toolset. Great for getting started in your journey learning about FPGAs.