My old 486 DX2-66 with 64MB of RAM and a 8GB HDD split into 4 2GB Partitions (roughly).
Internet is okay for light surfing, but doing facebook is impossible, their server just won't take requests from anything that's not Windows NT. E-mail works great through my super-old copy of Outlook Express, and out of all the browsers Opera 3.62 is the one that does the best. It seems to visit everything in at least a reasonably functional state. I have even posted to some modern guitar forums on that rig (should visit Vogons on the 486 one of these days). I'm currently messing around with flash plugins, and have come ridiculously close to getting YouTube working, I got it up to the loading circle in I think either Opera or IE a few times.
I have CD-Burning capabilities through CDRoast, I have WinPlay3 and WinAmp for MP3 and CD playback, oddly it's the ONLY computer in the house that will play my old Demo CD's from the early 2000's, so I might have to consider ripping those on the 486 (strangely I keep finding legitimate uses for old tech).
Once I get a DVD Decoder card, DVD playback will be possible if I install a DVD Drive. I also have a TV Capture card so if I really really wanted to I could play Atari 2600 and NES games through this particular setup, or even leech off the cable box. Old stuff for entertainment from Ebaums World or Bored.com still work, but things far more advanced don't.
About the only shortcomings is the occasional GEneral Protection Fault due to Windows 3.1x's wonky memory management. Even then, I might be able to update my Himem.Sys with a newer version and take advantage of having 128MB of RAM assuming WFWG has no limitation on RAM size itself.
Other entertainment, NES Emulation is possible, If I upgraded to a DX4-100 and a better sound card, Z26 could emulate Atari games. I still do a fair bit of NES ROM Hacking on the 486 (I Like the DOS version of Tile Layer and HExpose over windows utilities), plus I have a huge library of DOS Games, and lots of productivity software that can be pretty handy such as Harvard Graphics 3.0 presentations, WP51 for document writing, Lotus 1-2-3 for spreadsheets, and If I really wanted to go crazy I use Graf-X II for graphics.
I always considered the 486 the center point, the tipping point for vintage/modern, especially with how much things are getting less climatic in upgrading these days. Depending on configuration, a 486 can tip either towards "lowly slow DOS Box only good for playing old DOS games" to "Holy crap I had no idea this thing could do this" modern capabilities. Some expensive and rare hardware of the time really helps tilt the scale in the "modern" direction more.