A.k.a. the Internet Archive wayback machine [L1 ]: Frequently the only way of retrieving information on web sites no longer on the net.
Not Tcl-related (that we know), but often very convenient for digging up old stuff. If a link to some code here on the wiki is broken because the site has disappeared, then the info may still be up in this archive.
lexfiend 16 Feb 2006 - It's also useful for finding older versions of existing content (i.e. time-travelling). To find all archived versions of, say, http://www.scriptics.com/ , simply go to http://web.archive.org/web/*/http://www.scriptics.com/ and take your pick.