GNUStep is still pretty much a work in progress (Also see GNUStepWeb for an attempt at a GNU based WebObjects framework). It attempts to implement the full NextStep APIs under the GNU public license umbrella.|
F-Script itself is "free" but it currently only runs under Apple software - OSX or WebObjects. If you don't have either of these available, then you're not gonna get far in trying the software. They do have plans to make a port available for GNUStep, but I don't know the time frame.
I posted the link more for the ideas exposed, rather than the specific implementation. It's not often you see the ideas of Smalltalk merged with APL/J. For those without OS-X or WebObjects, it's more of an inspiration of how things can be, rather than how they currently are.
BTW: Information is available on WebObjects but I don't see any reference to a trial edition. I've heard very good things about the framework from the Apple community, but have not had the advantage to use it. IIRC, there was an NT version of WebObjects but I'm not sure of the current status.