Evening all.
To answer the OP, yes, Mumsnet is for parents of all genders and of all ages. And, actually, we do have a fair few members who are not parents at all, either because they are pregnant or hoping to become pregnant soon or because they are interested in our discussions and wish to reflect their own viewpoint.
We chose the name Mumsnet simply because it is a less clumsy, more memorable name than Parentsnet ever could be. Realising that the name might provoke exactly the same reaction as the OP is having, we then very deliberately chose the strapline "By parents, for parents" in order to signal our wish not to exclude fathers - or indeed grandfathers or even fathers-to-be.
We do take gender equality seriously - and we would never refuse membership to anyone on gender grounds. Men are just as welcome on Mumsnet as women, and, as many of you have already posted, we do have many male "regulars", ranging from stay-at-home dads to fathers-to-be to male nannies.
That said, we do think there is space on the web for forums where women tend to make up the majority of members. There is certainly no shortage of male-dominated forums...
But whatever gender our members are, we're very proud, over the years, to have built up a membership who are so willing to support each other so generously through the often tricky journey that is parenthood.