Ask HN: Want to set up a niche social network

I want to setup a social network for a very particular niche Im interested in. Ideally something with web, IOS and Android apps for sharing chat and images. So rather than reinvent the wheel Im wondering what hosted, open source or otherwise solutions are out there people might know of? Please no comments about why I want to setup another "facebook for cats"! I have a very specific idea Im looking at.