people have been accumulating several decades of experience with cweb, and we know that ctangle and cweave work reasonably well on numerous platforms. in general those programs are now entirely stable: don knuth won't be changing them any more, because they've proved their value in extensive use. (henceforth he must devote full time to the art of computer programming!)
however, further significant developments, including versions that don himself does not maintain, are ongoing. all of the really current news about cweb is, in fact, now to be found in this cweb development project. Check out the details in the releases description.
besides for further development, this ‘project’ is used as an – obviously incomplete – repository of original release versions of levy/knuth cweb. you can either compile these sources directly or stick the recent version “cweb-4.3” into my cwebbin, which introduces convenient extensions and prepares cweb for inclusion in the “tex live” distribution.
recently i spotted versions 2.7 and 2.8 in utah – and there's even "the" original cweb 2.8 in stanford –, but the intermediate versions 3.0 and 3.1 are still missing in my collection. i could scrape them from amiga a/o atari archives, but i'd rather have the respective originals. in case you can direct me to appropriate archive servers, i'd be really grateful.