Use Digital Research DR DOS if you don't like Microsoft. I have retail copies of MS DOS 5.0 on 5.25" floppies from 1991, and MS DOS 6.22 on 3.5" floppies retail from 1994. NSA\CIA\FBI etc don't have a time machine and can't time travel and insert malware into the base system retroactively.

DOS is a Single Tasking 16 bit Operating System programmed in x86 assembly; only 1 process on the top of the stack at a time. No keyloggers, runs in 384 KB of memory.

You'll have to audit 2-3 pieces of software ( a driver for a 3com or Intel NIC, and links 2 browser ) and compile using Borland Turbo C, or get a GCC compiler for DOS.
www.delorie.com/djgpp

Get a 486, or 386 with 16MB RAM install DR DOS or MS DOS, a NIC, a packet driver and the binary for Links, or compile it your self, set it to route through port 9050 on your tor router (running on Linux/UNIX). With that you'll be free to post whatever you want, nobody will know what you're doing on your computer, and if tor (or whatever comes next) works properly, then you'll be anonymous.

Free to read what you want from the internet, and post what you want to the internet.

>But but it's not FREE software,
> It's not GNU.
Precisely, I don't get copyright (legal) freedom, but I get actual (physical) freedom in the real world.
> But you could download an exploit; your system isn't secure.

Don't download and run anything from the internet on the DOS computer if you want it to remain with integrity. Just text reading and posting. Use it as a communications tool. Build a different computer for DOS gaming or use DOS Box on Linux/UNIX.