If someone wants their book to appear in a foreign edition, perhaps, or an audio format, they put its details up there and hope that someone comes along to buy those rights.
Agents sell rights for their author clients. They don't use a showcasing site like this because they have contacts, and co-agents who do the job for them.
I think it's going to fill up with self-published writers who want to sell foreign editions. But as there won't be many people registering who want to actually buy anything, just people who want to sell something, it'll all collapse in a heap before too long.
I remember getting promo for Sparkabook over a year ago, so it's not a new site. As Old Hack says, it seems to be mainly populated by self-published and small press writers...but not, apparently, by buyers.