LetterPile is a niche site for HubPages. It is a permanent 'new' website that has a specific theme and topics within it. There are about twenty niche sites today. HubPages is moving Hubs from this main site to those niche sites where it is said they perform much better. They are moving the creme of the crop that are quality Hubs and perform well regard traffic / views received. There is a long story why they are doing niche sites, but basically it is a business strategy lateral move.
Letter pile can be found at https://letterpile.com/
The theme for it is Writing and Literature. It includes subtopics:
Newspapers & Magazines
Here is a link to the announcements in the Forums: https://hubpages.com/community/forum/136386/letter...
You can go to the HubPages Blog by searching it on the web. When I post a link it doesn't seem to work. Oopps! :-) There you will see much more information on the niche sites.