Alpha Phi Omega National Service Fraternity, founded 1925 (
www.apo.org) is much larger than the two sororities. It has about 300 active chapters.
Gamma Sigma Sigma National Service Sorority, founded 1952 (
www.gammasigmasigma.org) has about 50 active chapters
Omega Phi Alpha National Service Sorority, founded 1953 (
www.omegaphialpha.org) has 28 active chapters.
All have both men and women members (like most Professionals, they are required to be co-ed by Title IX).
All of these are collegiate organizations with the primary unit being on the college campus, but with Alumni Associations of those who became members in College.
I'm an alumnus of Alpha Phi Omega and know members of both other groups. I've got considerably more information, but until I know what school you are at, and other questions, I'll hold back.
