Together with hardware that can bring RF signals into digital form Linrad forms an SDR receiver. (A Software Defined Radio receiver.) There is also a transmit part inside Linrad that will form an SDR transmitter together with appropriate hardware. (The transmit side is still at an early development stage.)
Although there is a learning curve initially, Linrad is without doubt the best performer in Software Defined Radio out there at this time. Not only is it completely configurable and highly developed, its performance is remarkable. You can pull signals from several db's below the noise floor, and at the same time, not saturate with a stronger signal. Filters are completely configurable on width rate and even phase, AGC is configurable for three independent factors, and you can calibrate it to allow for quirks/deficiencies in individual hardware. It doesn't have a "traditional radio" interface, but it is well worth the time to get to know - and the interface makes much more sense given the nature of the job it's actually doing, not trying to copy.