Still not sure where I should post SINGLE-Player rpg requests. Here they tell me to go to MMORPG request. There they tell me to come here... So I just alternate. ANYWAYS

Are there any games which go along with the stealth-type thing of Hitman, Theif, and other games? That are free and downloadable, of course. And single-player.

Ugh.
If you are talking about PC; NONE ARE FREE.
And if you are talking about consoles; guess what.
Not free.
Sorry to say, but your in bad luck. Most hitmen/assassin games are pay to play or buy to play.
If you have money; try buying Hitman: Bloody-Money. ( fun game even though the AI system is sort of stupid )