Companies can be really big and it's hard to generalize. We can all say something nice about our current companies, I'm sure. But if you're thinking of interviewing places, I think it's pretty easy to anticipate when a place will be female friendly.
- If there are powerful women in the company in upper management.
You can bet that these women will have zero tolerance for a hostile environment or sexual harrassment. I worked for a gaming company once; I was the only female engineer in a room of 40 people and the product designers as part of their presentation revealed new character sketches with highly sexualized images of women. Then they said flippantly, "Sorry to all the girls in the room." Everyone looked around. If a female CEO was there it wouldn't have been tolerated.
- If you have women as your coworkers and they seem happy and have had growth opportunities.
During your interview, just ask! The best correlation to being satisfied is asking whether the people who work there currently are happy.
- If the company makes products popular with women
A little speculative, but I think I would love working at Pinterest. Especially in the beginning, men just didn't get it -- and women loved it. Having a passion and domain knowledge for your product will make you an incredible engineer with a huge advantage over people who are just thinking, "what are we doing, I have no idea if customers will like this or not," and if you're determined to go up, it'll help you get there.
This is going to get a bit snarky and controversial, but I'm moving along...
- If the men you work with are really attractive and awesome and funny and great at their jobs and have great girlfriends.
The chances of sexual harassment is almost zero. People don't hit on their female coworkers unless they're awful. or desperate. or sleazy.
- If anyone at the company has in the past dated or is currently dating their coworkers.
Heavily implicates bad management that tolerates fraternization and an unsafe, unprofessional work environment.
- (if you care about work-life balance) they have a flexible work from home policy and taking long breaks from work is tolerated.
If you plan to take maternity leave or have odd hours and leave at 3pm daily, work at a bigger company that's more relaxed, because it's very hard to be aggressive at highly competitive companies if you do care about that balance.