LoS tools is a QGIS plugin written in Pythonu. It is available directly from QGIS plugin repository. The plugin provides mainly processing tools focused on visibility and its analyses using so called lines-of-sight. Documentation for individual tools is on website.
There are more then 15 tools focused on line-of-site construction and analyses as well horizon identification and processing.
The plugin is an interation of older tool Line of Sight Analyst implemented in open source GIS.