Been trying Dungeon Runners, no follow and lots of alt tabbing but its just about doable... if you're really into the free thing.

You could also go with EVE Online which while you do have to pay you can if you work at it enough pay for playtime with the in game currency. And I know a couple of people who fund several accounts from their ingame currency creation... of course the multiboxing is a little different and far more macro management (not macros, though having those helps too).