Cryptomator

Multiplatform transparent client-side encryption of your files in the cloud. You need Java 8 in order to run the application. Get the runtime environment here: http://www.oracle.com/technetwork/java/javase/downloads/index.html

If you want to take a look at the current beta version, go ahead and download Cryptomator.dmg, Cryptomator.exe or Cryptomator.jar.

Features

Totally transparent: Just work on the encrypted volume, as if it was an USB drive
Works with Dropbox, OneDrive (Skydrive), Google Drive and any other cloud storage, that syncs with a local directory
In fact it works with any directory. You can use it to encrypt as many folders as you like
AES encryption with up to 256 bit key length
Client-side. No accounts, no data shared with any online service
Filenames get encrypted too
No need to provide credentials for any 3rd party service
Open Source means: No backdoors. Control is better than trust
Use as many encrypted folders in your dropbox as you want. Each having individual passwords

Default key length is 256 bit (falls back to 128 bit, if JCE isn't installed)
PBKDF2 key generation
Cryptographically secure random numbers for salts, IVs and the masterkey of course
Sensitive data is swiped from the heap asap
Lightweight: Complexity kills security

I/O operations are transactional and atomic, if the file systems supports it
~~Metadata is stored per-folder, so it's not a SPOF~~
NEW: No Metadata at all. Encrypted files can be decrypted even on completely shuffled file systems (if their contents are undamaged).

Distributed under the MIT license. See the LICENSE file for more info.