TL;DR:
You can invite people to add to your collection. Not "anyone can submit", specific people you picked.
Invite only, by username. An invite expires after 7 days if it isn't accepted.
Two roles. Contributors add items. Managers add items, invite more Contributors, and review submissions.
Up to 25 collaborators, 5 of whom can be Managers. Pending invites count toward that.
Whether items need approval is your existing collection setting, not a property of the role.
Open it to everyone and keep review on, and anybody can submit while your Managers decide what makes it in. A collection curated by a few people and filled by the community.
The owner needs a membership. Collaborators don't. If you're invited, you just accept. No Buzz involved.
What changed
A collection used to have two settings, and both were blunt. Keep it to yourself, or open it to everybody. There was no way to say "these six people can add to this."
Now there is. Invite people by name, give them a role, and the collection becomes something a group builds.
The two roles
Contributors add items, and can remove the items they added.
Managers do that, plus invite more Contributors, review submissions, remove anyone's items, and edit the collection's name, description and cover.
You, as the owner, are the only one who can hand out or take away the Manager role, and the only one who can change the collection's privacy settings. A Manager can't promote someone to sit alongside them, and can't remove another Manager.
How inviting works
Search a username, send the invite. They get a notification and an invites inbox, and they accept or decline. An unanswered invite expires after 7 days.
The cap is 25 collaborators, up to 5 of them Managers. Pending invites count toward it, so a stack of unanswered invites holds seats until they lapse.
Bookmark collections can't be collaborative.
Whether contributions need approval
That's your existing collection setting, not a property of the role. If your collection accepts submissions immediately, a Contributor's item appears right away. If it's set to review, their item waits, and you and every Manager get a notification that something's pending.
The combination worth knowing about: open the collection to everyone and leave review on. Now anyone on the site can submit to it, and you and your Managers decide what actually lands. That turns a collection into something a few people curate and everybody fills, which is a different thing from a private list or a free-for-all.
One limit to be clear about: approving is a Manager job. Contributors add their own items and can pull their own back out, but they don't review other people's. If you want more hands on the queue, promote people to Manager.
Either way you can remove anything at any time.
The membership part
Inviting collaborators needs a paid membership, any tier. The people you invite don't need one. They accept and start adding, whatever their account is.
If your membership lapses, the collection doesn't disappear. New invites stop and submissions close, and people already collaborating keep the access they have. Resubscribe and it picks back up.
Collaborating costs no Buzz. This one is a membership perk, not a purchase.
Tell us what you think
The caps and the 7 day invite window are guesses. If you're running something that wants more than 25 people, or you're inviting people who take a fortnight to notice a notification, say so in the comments.