i would like to know which toolkit is used in Lazarus IDE (linux version) ? It isnt gtk ? Or maybe ... other ? Thanks
There are multiple possibilties, GTK2 or QT. Older versions also supported GTK1. There are unfinished efforts (LCL-FPGUI) to build directly on top of X11.
Most distros tend to ship the GTK2 edition though
This partially also QT requires a "flattening" library called qtinf (sometimes also called QTPAS), which wraps C++ QT in C, so it can be called by Pascal.