DOTT is a really fresh game. The graphics are poor when compared to what is available now, but it is still cute. The basic concept is simple: The game starts when you learn that, just the day before, one of the professor's tentacles had drunk polluted water and mutated to a power-mad tentacle, now with arms. (Shock and horror!) The professor wants to teleport you and 2 friends a day back in time to prevent it from drinking the water, but predictably something goes wrong, and you stay in the present, while one of your friends is teleported 200 years into the future, and the other 200 years into the past.
Your friend who now lives in the past has the opportunity to talk to Benjamin Franklin, George Washington and the likes, watch them sign the declaration of independence and so on. The friend in the future is caught in a world where tentacles rule everything, and humans are slaves. Your job is to coordinate these 3 players and find a way to (a) stop purple tentacle from taking over the world and (b) repair the time machines so your friends can get back to the present.
You can play any of these 3 characters, and you have to swop between them often in order to play the game. The gameplay is good, replay value is pretty low since there's only 1 story to figure out and once you know what to do most of the fun is over.
I enjoyed it, probably won't play it again though so I don't know if it's worth the money to buy it. It's getting to be old now though so you might find it on abandonware somewhere.