We use yammer here, for the whole company but with subgroups by department/interest etc. Works pretty well. We have tech subgroups where we post about project launches/new products/training/blogs, but there are also groups for general company info, starters/leavers, social events, office admin groups etc. Threads are started for leavers and joiners, baby news, food discounts in the area. It's collaborative and doesn't require one person to collate everything into a newsletter.