Vanilla splitscreen lol

[duh]

[jmickle66666666]

you could set up the controls of each to use completely independent keys, then use a utility like joy2key to map the keys to the controllers.

[duh]

[Bucket]

If you're not too concerned with running vanilla (which I imagine you're not, as you're using DOSbox), Doom Legacy has native splitscreen support.

http://doomlegacy.sourceforge.net/

[Tango]

I think ReDoom might also have splitscreen? maybe