Delicious has just announced 4 new features to make its stacks, or collections of links, more social. Because the only thing better than a bundle of your favorite kitten websites is bundle co-created by you and your friends. Users can now collaboratively build stacks, comment on whole stacks, respond to a stack with a stack similar to a YouTube response, and create private stacks. The features will permit new use cases like stealth cooperation and challenge products like Facebook Groups and Pinterest which already support privacy and collaboration.

The collaboration feature lets you invite friends to edit your stacks. This could help teams cooperate on research, or let friends compile a set of favorite links around a topic.

Commenting on entire stacks lets you have conversations about the interconnections between links. You can also suggest links you think would enhance someone else’s stack.

Stack responses lets you battle over who can find the best content around a topic, or offer a contrasting collection. For example, if you’re worried your friends might actually buy something from their Atrocious Sweaters stack, persuade them not to ruin their image in the name of irony by responding with a stack of stylish sweaters.

Private stacks make Delicious more than just a broadcast channel for your taste. You can stealthily collect links and curate them before publishing to the world.