My travels have taken me to a few, but not many. They're always interesting, though.
As a sort of opposite to Octoberfest, check out Munster's Germanfest. Usually in the Spring, around April/May. It's a neat town, and a sort of typical Octoberfest-style festival. But, in the Spring!
Some odd-ball festivals I've stumbled across as well:
Lamesa "Chicken Fried Steak" festival. Don't expect good CFS, but it is a neat festival if you happen to be in the area. I don't think I'd go out of my way for it, though.
On the other side of the state, the "East Texas Poultry Festival" is interesting. Apparently it just passed, though.
Texas Scottish Festival and Highland Games. Have not been in a number of years, but in the past it was a great time. I think they've had some difficulties of late, so not sure if its still a thing. I believe there is an Irish equivalent, but idk much about that one.
Poteet "Strawberry Festival" in the Spring. Have not been to it myself, but have heard good things.
Parker County "Peach Festival". It's neat, but its always way too hot. Beginning of July, on concrete in downtown Weatherford. If you don't mind the heat, it's worth checking out.
I'm hopeful more traveled people than me can chime in. It's an interesting thread, and I'm guessing there are dozens of great community, music, food, etc...festivals all over the State that few know about.