Notes app with a local synchronization feature. This way all your notes will never leave your local network. The Desktop Version of the app could discover the app other computers or on mobile device and you could link them up and synchronize notes between them. 
You could organize the nodes in folders and sub-folders - like the files on your computer. 

The Android Version has some extra features:

You cold hide some of your notes and make them visible by searching the title of the note. 
You could encrypt your notes and after you enter the password again - you could read the encrypted notes. 
You could use your voice to enter your notes - thanks to Google Voice. 
You could enter text by hand drawing the numbers and letters - with an extra feature to add special gestures that will input not only letters, but whole words or sentences. 

You could use your camera to read and record the text from an image or the outer world. This functionality is not 100% successful. It is more high quality with black text on a white background.