Launched in early 2016, the Writer's Ark discussion forum is intended as a looser and more focused spiritual successor to AH.com's now-defunct cousin forum, Counter-factual.net. It was established thanks to a joint effort between Midgard and Doctor What, as well as several other veteran members of both AH.com and C-F.net.
This discussion forum is aimed primarily at fostering writing and posting of stories, and discussions on conceptualising, writing and publishing various fiction. This includes speculative fiction genres, of course. Though not specialised primarily in alternate history fiction, AH is one of the many genres you can discuss over there, in the capacity of an AH writer.