My mind was almost literally blown when I found that org-mode in emacs has this. I believe you have to be putting in the noweb comments, but there is a detangle function.
Wow nice. Found http://comments.gmane.org/gmane.emacs.orgmode/32814 but I'm not sure the workflow is as convenient as syncweb. Syncweb has a unison interface to synchronize which allows to very quickly synchronize many chunks automatically. Syncweb can automatically know in which direction things need to be synchronize. If one modify the code, then the synchro will update the org, if one modify the org, then the code will be regenerated. If one modify the org, and the code at the same place, then a conflict will be detected.