Nooface blogs Fluid Documents.(They link to the Hypertext '98 paper; the Hypertext '01 paper is even better.)
Nooface links to TreeDoc, a stretch-text implementation for the Web written in PHP. It seems to me that TreeDoc is only peripherally related to Fluid, and it lacks any of the finely-honed animations that Zellweger et al. consider so important. And when Bill Softky, the implementor of TreeDoc, claims that "the in-line method of hypertext display was originally conceived by the Fluid Documents group at Xerox PARC", he's simply mistaken: its history obviously goes back to Peter Brown's GUIDE in the mid 1980s. I'm quite confident the Fluid folk know this!