Even that leaves a lot of room. If you can fix certificate problems, any simple browser (even text mode lynx) can still do a lot these days. But let's go reall

Even that leaves a lot of room. If you can fix certificate problems, any simple browser (even text mode lynx) can still do a lot these days. But let's go really "modern", i.e. being able to access web applications without missing features, timeouts etc. Slower, maybe just one at a time, but what you do works. That's surprisingly hard. I sometimes use TenFourFox, a browser for Power Macs, which is a bit of a mashup between older versions that were still supported and back-ported newer features. And that can run on a quad core G5. I'd say that still misses the mark, but might come close enough. With a G4, that would bring you to maybe 2002's tech. But in the end, for a lot of modern stuff you're basically required to have an "Evergreen" browser or IE11. On Windows, that means Windows 7, which IIRC won't run on Pentium IVs and requires about 1 Ghz/1 Gig RAM. So 2005/2006's tech. On Linux, you can go lower. There's still 32 bit Linux support for Firefox, so if you can get a recent enough distro on an old computer, it should work. A core solo definitely does, and I guess a souped up Pentium IV should work well enough, too. Beyond that, it's going to get interesting. Pentium II's should work and you can give them enough RAM to chug along with a recent OS. So that' about 1998/1999. Beyond that, CPU speed and max RAM will result in some breakage.