Features available from Tk. This page is a companion piece to the Tcl Portable Runtime Library.
XLEL: the Xlib emulation layer. If you need to draw graphics cross-platform, this is for you. (Note: there are other approaches to this also, but they are not in the core: TkGS, NexTK)
DKF: Note that the emulation layer also hides virtually all the differences between different platforms relating to event handling. The only tricky bit is that some platforms simply don't deliver all the events that real X11 produces.