Summoner: One Man Army

Alexander O'Brian was a pretty normal, if particularly antisocial guy, but when he finds himself in a stone room with no visible doors or windows with floating boxes saying that he and 10 million other people have been selected for participation in a tutorial, and that three days after it ends dungeons will start appearing on earth and spitting out monsters if they aren't cleared fast enough, he will have to seize every advantage he can grab in order to survive and thrive in a rapidly changing new world.

Note: This will be somewhat slow paced, so any timeskips or level jumps will be few and far between.