In my city, various groups sponsor events like these many times per month. Some groups say "women only" for some of the events, while others make it clear that everyone is welcome except for heterosexual men. The postings don't mention a reason, although sometimes they'll mention that it is a "safe" environment.

This offends me on several levels. One is, this is a type of job training.

On the other hand, I do have some mixed feelings about the subject, because women have historically not been active in computer science.