From the README:

SoXt is an open source implementation of the SGI InventorXt library, which
is a GUI binding for using Open Inventor with Xt/Motif.  While SoXt has
been developed for use with Coin, it is also possible to compile it against
Open Inventor from SGI or TGS.  A goal is to eventually become 100% source
code compatible with the InventorXt library, which is still way off,
especially when it comes to creating derived classes.

When using SoXt, bear in mind that SoXt is in its alpha release phase,
so expect the worst...

WWW: http://www.coin3d.org/