KHTML is a discontinued browser engine that was developed by the KDE project. It originated as the engine of the Konqueror browser in the late 1990s, but active development ceased in 2016. It was officially discontinued in 2023. Built on the KParts framework and written in C++, KHTML had relatively good support for Web standards during its prime. Engines forked from KHTML are used by most of the browsers that are widely used today, including WebKit and Blink
If I remember correctly it’s under a copy left license which makes sense given it’s ultimately a derivative of KHTML.