Windows/Mac/Chrome: Encrypted cloud storage services aren't difficult to find, but when you need to send a file to someone else and you want to make sure you keep some control over it (and it stays encrypted), you have fewer options. Peerio is a new free service that wants to make that whole process easy.
The video above gives you a quick primer of how the service works, and why it's important to control your own encryption. Peerio never gets your keys, so it can't decrypt your files. Similarly, when you share a file, you have to share it with another Peerio user, and you essentially give that user permission to decrypt your file with their key as well -- which again, Peerio doesn't have access to. All of your files are encrypted before they leave your computer, and they're encrypted in transit before they sit, encrypted, on Peerio's servers.
Peerio is more of a secure messaging and file sharing service than a cloud storage solution -- you only get about 1.3GB of space for signing up. Messages sent back and forth between users work like IMs, and you can see where your files go after you've sent them. You can see when they have been opened, and at any time you can "destroy" them, so any user who has them in their inbox has them deleted and their permissions revoked. The Chrome app supports message and other notifications in real-time.
The service is from the same folks behind previously mentioned Cryptocat, and while the service is currently free, they plan to add paid features in the future. Mobile users: Android and iOS apps are on the way soon. Hit the link below to learn more.