I don't want to write any of those, but I could give a decent idea for an Azkaban!Harry. Azkaban has become one of the Dark Lord's outposts some time during Harry's Hogwarts years (sixth to seventh year). Harry graduated and was immediately drafted as an apprentice in a special Elite Auror force. The war by this time had become a brutal stalemate where both sides can't get a decisive victory. In an attempt to sway the favor towards the Ministry the current Minister (some strong and powerful strategist personality) sends the Elite Aurors to recapture Azkaban. Harry, as an apprentice, also gets to go. The battle is won but many die. Among the presumed dead was Harry Potter. The surviving Death Eaters are then detained in Azkaban with Auror guards. With Harry's obnoxious stream of bad luck, he gets stuck in Azkaban as a prisoner. Since now it is only guarded by Aurors, it would be easy for someone who trained among the elite to escape. He does and starts a vengeful streak for his temporary sabbatical at Azkaban. Then it becomes a Dark!Harry where he has a list of people he has to kill and at the top his to-kill list is the Minister. He becomes an unknown factor in the war and is finally labeled a Dark Lord (due to his remorseless killing of the innocent who get in his way). The wizarding world then has to contend with two Dark Lords. This is as far as I could go. Anyway, this idea might be a sucker but I haven't seen anything like this yet.