[ipsun4]

Depends on what you want out of a computer. If you want a general purpose (as in write programs and run them) Plan 9 is a pretty self-contained operating system and software system if you are confident in your C and C++ abilities. I've also heard that BSD is pretty well documented internally, so if you know that system, you should be ok.

Alternatively a fun retro setup could be an apple II or a windows 98 box with Encarta disks.

As a specific distro that is directly focused on what you specified, Endless OS seems to have the Encyclopedia and other preinstalled apps for online use you were talking about.

[karmakaze]

Which leads to another interesting take on the situation. Which OS would make a good starter to rebuild from? It should be small, easy to build, and cover just core features including network. Even single-user, single process like Windows 98 as suggested could work, although we'd want much newer source without cruft. The GUI also seems superfluous--maybe just high density text panes.