Slingshot is an interesting new app from Facebook that lets you engage in a sort of ongoing photo trade with friends and family. All you have to do is send off a photo when you're doing something fun; and when they're ready, they'll do the same.
Auto-Sync contacts: You can only send Slingshots to fellow program users, but the app does make it easy to find them. It can import all of your Contacts as well as all of your Facebook friends and let you know who already has an account in just a matter of seconds. And you can send invitations to friends you'd like to share photos with straight from the app.
Immediate reactions: When you receive a photo, you have the option to immediately react. Choosing that option opens the self-facing camera, and you can show your friends in one image exactly what you think of the photo they just sent you.
Send to reveal: You can't see photos that have been sent to you through this app until you send one back to the sender. And they can't see the photo you just sent until they send one back to you. While the idea behind this design is interesting, it can quickly cause the photo exchanges to turn into an unending back and forth of unexciting photos just so the sender can get a look at what they just received.
Reaction review: When you take a Reaction photo, it's immediately sent. You get no chance to review it, and so you can often wind up sending a reaction that wasn't really what you were going for.
Slingshot has a lot of potential, but it does have a few kinks to work out as well. However, if you understand the intended purpose, and the people you're using it with do as well, it can be a lot of fun to use -- and it's completely free.