The LSL distribution consists of the core library and a suite of tools built on top of the library.
The core transport library is liblsl and its language interfaces (C, C++, Python, Java, C#, MATLAB). The library is general-purpose and cross-platform (OS Support: Win / Linux / MacOS / Android / iOS; Architecture Support: x86 / amd64 / arm).
The suite of tools includes a recording program, file importers, and apps that make data from a range of acquisition hardware (see Supported Devices and Tools) available on the lab network (for example audio, EEG, or motion capture).
There is an intro lecture/demo on LSL (part of an online course on EEG-based brain-computer interfaces).