Final answer:
Two other types of fraternities besides social fraternities are professional fraternities and honor societies, with each focusing on professional development or academic achievement, respectively.
Step-by-step explanation:
Aside from social fraternities like Sigma Pi, the other two types of fraternities are professional fraternities and honor societies. Professional fraternities are designed for students in the same professional field or area of academic study and focus on networking and professional development. In contrast, honor societies recognize students who excel academically or as leaders among their peers usually within a specific discipline.