Noweb is like #web and #cweb except is language-agnostic and very minimal. #Web being the Pascal-oriented system in which Knuth wrote his spaghetti code for TeX and Metafont, and #CWeb being a similar system for C.
(I once made a very minor contribution to cweb, btw. Support for ‘huge’ mode in Borland/Turbo C for MS-DOS.)
Another difference is noweb can go to multiple different pretty printers, at least these days.