Casper

Casper is an alternative client for Snapchat whose most important feature is that it lets you save images from other users, without them knowing. Snapchat normally tells other users when you try to take a screenshot of their pictures, but you don't have that problem with this client.

Another interesting feature in Casper lets you forward stories to other Snapchat users. If you really liked a picture a friend sent you, you can forward it to your other friends. You can also add lots of stickers and filters to any picture you take, and really easily, too.

The only inconvenience in Casper is the identification process. Before you start using the app you have to identify yourself with your Snapchat login, and then Google's. Even the app's developers recommend logging in with an alternative Google account (one you don't normally use).

Casper is an interesting and alternative Snapchat client, mainly thanks to its useful features. In some respects it's inferior to the official client, but the option to save pictures from other users without them knowing makes it by far more interesting.