Librtlsdr is the backend used by most SDR applications compatible with the well-known RTL2832U demodulator. Using librtlsdr, you can get raw I/Q samples from RTL2832U chip, thus turning a cheap TV stick into a software defined radio (SDR).
Librtlsdr source code can be found on GitHub. It compiles easily on Linux hosts using instructions from Osmocom project. Compiling librtsdr on Windows is not that easy, mostly because the only two required libraries (libusb and pthreads) cannot be located using the same methods as on Linux (pkgconfig).