For example, the United States Marine Corps is slowly integrating some basic training and has a few co-ed companies [1]. This was such a far-fetched idea in the 90s that Ridley Scott made a movie about it starring Demi Moore (G.I. Jane, 1997).
Firefighting is another excellent example [2]. 7-11% of firefighters in the United States are women (depending on how volunteer vs. career firefighters are counted). I remember that statistic because StackOverflow's female respondent rate hovers around ~5%. "Women are more likely to run into burning buildings than what I'm doing now" is the kind of gallows humor that gets me through the day.
There are also advocacy groups for other gender/work minority combinations, like male nurses and caretakers.
[1] https://www.hqmc.marines.mil/Portals/61/Docs/FOIA/Reading-Ro...
[2] https://en.wikipedia.org/wiki/Women_in_firefighting
Edited: typos