Darkover series
The Darkover world is a science fantasy series by Marion Zimmer Bradley, in which there are fantasy-like elements (psychic magic, swordplay) which are (within the series as a whole) rationally explained. There are several gender-related elements in the Darkover world. First, the society which was separated from the rest of the Terran universe developed a patriarchal structure in which women are oppressed. Within this greater society there are sub-societies: the Dry-Towns and the Free Amazons. The Dry-Towns are a combination of Muslim society and John Norman's Gor novels, with women literally kept in chains and owned by men. The Free Amazons of Darkover are an all-woman society which pledges to live without attachment to men and to be self-sufficient. Beloved by many, the Free Amazons are a model to many of a woman's society within a greater mixed-sex society: fully independent and self-sufficient, fairly democratic and non-compulsory, and sexually free.
A second gender element in most of the later Darkover novels (later in the Darkover chronology; not later in publication date) is the clash of cultures between the traditional Darkover society and the Terran society, which is nominally egalitarian but in reality is still very patriarchal.
Third, there is a strong feminist element in most of the relationships depicted in all the novels: women are shown as strong, rational, capable human beings, suffering under oppression, and fighting back or rebelling in many ways.
Finally, from the mid-1970s onward, homosexuality came more and more out of the closet in Bradley's works, and many of the later Darkover novels dealt directly or indirectly with issues of gender role conformity and sexual orientation.
The Renunciates: Free Amazons trilogy within the Darkover series most directly deals with gender-issues, in that the novels focus very clearly on all three elements described above. These three novels (The Shattered Chain, Thendara House, and City of Sorcery) all deal with aspects of feminism in a patriarchal culture. The Shattered Chain deals directly with the role of women in Terran and Darkover cultures. Thendara House concerns conflicts of culture, gender, and justice. And City of Sorcery is a traditional quest story in which a Terran-gone-native travels with her female lover to discover the secrets of the Society of Free Amazons. In Heritage of Hastur, a young gay aristocrat is the protagonist.