Great work.
I cannot read on the homepage about
- macOS Cocoa widgets support
- Linux Gtk2/Gtk3/Qt5 support
- Haiku support (Lazarus does it via Qt5, Haiku has Qt5)
MSEgui is a complete independent fpc Pascal widgetset.
It does not use any other widgetset like Gtk2/Gtk3/Qt5.
MSEgui interact on Unix directly with X11 server (like others widgetset do).
For Windows, it deals with low level Windows gdi interface.
In fact,
MSEgui is a Gtk2/Gtk3/Qt5 widgetset but much better and totally with same aspect on each OS, this if compiled on Linux, Windows and FreeBSD.
And because it is developed in Pascal, you have full control on the widgetset.
I did not try
MSEgui on Haiku but if Haiku uses X11 graphic server (or Wayland) it should work too.
For Mac,
MSEgui is not yet compatible, sorry.
Fre;D