Turtl is a note taking app. What sets it apart is that all the data is encrypted from syncing it with the companies servers or you can setup your own internal server. This makes it a great alternative to the plethora of note taking apps such as:
The encryption used in Turtl (At a glance to me (Not a Crypto expert)) seems to be relatively secure as it uses SHA256 and individual keys for each piece of content full technical details at their user documentation explaining the algorithms in use and how they are applied (Encryption specifics). the organisation of your notes are using boards which can be shared with other users securely.
Overall it makes your life more secure and also keeps your information private. The project is at its early stages and is maintained by a small group of people in their spare time but looks very promising and something to consider if you want a secure place for your notes.
Turtl can be download from Here