In a 5- or 6-qt slow cooker, stir together beer, orange juice, chili powder, cumin, oregano, salt, and cayenne. Add steak, turning to coat well. Cover; cook until steak is very tender, 4 to 5 hours on High or 8 to 9 hours on Low.
Transfer steak to a cutting board; cut crosswise into 4 pieces. With two forks, shred steak.
Lay tortillas on a work surface. Divide steak evenly among tortillas; top with tomatoes, onion, and cilantro. Serve with hot sauce.