http://indispensibletools.pbwiki.com/
I wouldn’t ordinarily thumbs down a resource site, however, many of the listings that are reported as *free* are not. Admittedly, some are great resources, but many listed are second rate, especially when compared to some of the truly free educational resources that are available on the Internet. In my opinion, that makes then dispensable tools.
Note, also, the improper spelling of indispensable. Not very scholarly.