I am actually working on a project to basically "retrofit" a lot of useful modern web pages and other web services for use in ancient browsers (I am doing most of my testing in Netscape Navigator 4.04) in order to make older computers and software more useful for modern tasks. For web I am mostly creating retro-friendly versions of web pages that have no javascript or anything for older browsers to choke on. This setup requires a sort of "middle box" (I am using a raspberry pi) to serve the pages and also terminate SSL/TLS connections (since virtually nothing SSL-related today supports the cipher suites that netscape and other older browsers use) as well as other intermediary tasks; I am basically using my own internal domain for these pages (maps.legacyweb.net, search.legacyweb.net, weather.legacyweb.net, etc.)
So far I am able to do email using my old client (I used pegasus; I think you should be able to use Eudora on a mac) and I also have a retro google maps that lets you search for places nearby and get directions and map images. I plan to do one for weather, news, and search among other things.
I also wanted to make AIM useable again, since this was such an integral part of my early Internet experience. AIM recently stopped supporting older clients as MD5 authentication is now deemed insecure. I started on a python program that basically mocks the OSCAR protocol that AIM uses, and can be used to serve other modern chat services such as jabber/xmpp/facebook/etc. I am about halfway done with the mocking of the protocol... I have login, but so far haven't implemented buddy list, etc.