It was launched in 2006 as an ebook community, but it took a sharp turn in focus in 2010 when it was bought up by a trio of publishers (Penguin, Random House, HarperCollins) and a retailer (HMV) with the goal of making it into a social ebookstore, a move that doesn't appear to have worked out as well as they'd hoped.
Just to put this into perspective, 2010 was the year that Copia launched as a social ebookstore. They didn't have much success either, and as a result Copia has since pivoted to selling their ebookstore platform to retailers (instead of Copia selling ebooks to customers).
The seller (HMV) in this story also used to own Waterstones. It looks to me like HMV had planned to tie Anobii into Waterstones as an ebookstore. That plan fell through when HMV sold off Waterstones last year, and it pretty much became an impossibility once Waterstones announced plans toin stores.
But for Sainsbury's this is still looks to be good news. It gives the chain an established, albeit small, presence in the market. Clearly Sainsbury's wanted to sell ebooks, and while they did have other options (Copia, Blio, txtr), buying Anobii generated both a lot of media attention and it also gained Sainsbury an ebookstore with social features as well as a higher degree of control. Copia could provide the former, but I suspect that Sainsbury's wanted the latter as well.
Curiously enough, HMV is described as having owned just under half of Anobii, and yet Sainsbury's now owns nearly 2/3. When you combine that with the sale price (one pound sterling), it makes me wonder if Anobii is a money pit, and that Sainsbury gained a controlling interest in exchange for promising to cover the costs out of their own pocket.