I heard Ultima IV was the game that changed the face of RPGs. It's available for free when you sign up for GOG.
Frog Fractions may not be a true text based game, but it has text based section. I tried when I heard about it on Giantbomb and it is hilarious. You can find that for free here: Frog Fractions | Twinbeard Studios
Tonight: Arrow comes back in a Flash, runs into Mob City, the Black Friday trilogy ends, Sports Ball is played.