I am an Alpha Phi Omega alumnus and on the National Alpha Phi Omega history committee and was representative to the APO chapter at Howard for a while. I'm probably able to give background on this better than most.
Timeline:
12/16/1925: Alpha Phi Omega founded. Membership limited to only men with Scouting (Cub, Scout or Leader) experience.
4/17/1947: First Alpha Phi Omega chapter founded at an HBCU. Johnson C. Smith University (Delta Phi - chapter #117). Howard University is second on 5/22/1948 (Zeta Phi - chapter #165).
1952: Gamma Sigma Sigma National Service Sorority Founded by eight women's service groups. Alpha Phi Omega brothers helped put the groups in contact with each other, but as far as I know were not at the meeting where the Sorority came into being.
1953: Omega Phi Alpha National Service Sorority came into being. Alpha Phi Omega service fraternity chapter at Bowling Green State encouraged women also interested in service to form their own group.
1950s-1970s: Some Alpha Phi Omega chapters continued to have local related women's service organizations integrated into the chapter in terms of service and social events.
1960s: By this point if not earlier many (if not all) Alpha Phi Omega at HBCUs were reflecting the way that the NPHC fraternities were doing things. They called their pledge classes lines, they called the pledge classes by a "club name" like AKA's Ivy Club or Kappa Alpha Psi's Scroll club. Alpha Phi Omega chapters often used the term "Trefoil Club"
1967: Alpha Phi Omega removes the requirement for prior scouting membership at its Constitutional Convention. Many chapters by this time had more or less allowed anyone to join, with those without prior scouting experience simply being registered with their local Scout Council as a volunteer in order to fulfill the requirement.
Late 1960s - Early 1970s Chapters from liberal schools and/or liberal parts of the country were pledging women "underground" and registering them with the National Office simply under their first initial and last name.
Early 1970s: Proposals to go co-ed first seriously raised.
1972: Title IX. All non-social Greek Letter Organizations required to go co-ed. (Note, this is why legally, the NPHC greeks no matter how much service they do are legally counted as social fraternities)
1974: After *much* debate, women are allowed affiliate membership in the Fraternity.
1976: After even more debate than in 1974, women are admitted as full members of the fraternity. As part of the "Gentleman's Agreement", chapters are not required to admit women, nor required to admit women brothers who transfer (Transfering membership requires the incoming chapter to accept them). This was to deal with those all-male chapters who considered leaving the fraternity if they were required to admit women.
1977-1979, a majority of chapters go co-ed. *No* chapters at an HBCU does so.
Up to at least1981: Efforts continute to attempt to get the law changed to have Alpha Phi Omega be exempt from Title IX.
1986: Chartering chapters and rechartering chapters are now required to attempt to recruit from both genders. This, to use a term from a brother from an all-male chapter "neuters" the all-male chapters. It also means that an all-male chapter that goes inactive must come back coed.
1996: All-male chapters make up about 15% of all chapters in the Fraternity.
2005: Opinion given by legal council that Alpha Phi Omega must not bar women from chapters any more. National Board resolution reflecting that passed.
2006: All-male chapters make up 17 of approximately 350 chapters in the Fraternity. National Convention (by close vote) supports National Board. All all-male chapters must co-ed by 2008 convention or show good faith in that direction or have their charters revoked for failure to follow National Pledging Standards and National By-laws. Committee formed including members of all-male chapters to help with transition.
I'll add specific comments on other postings separately.