UPDATE 2024: Get a new version here: https://github.com/ivoras/EncryptedNotepad2
"Encrypted Notepad" does only one thing, but aims to do it perfectly - a Notepad-like simple text editor where files are saved (and later loaded) encrypted with industrial strength algorithms. Available both for the desktop (as a Java application) and on Android.
JCryptor is an encrypting tool based on the Caesar-cipher.
...ROT13 can be decrypted by encrypting it again with ROT13. Even today this simple method is used by authorities to protect documents from unintentional reading.
--UPDATE--
[25.01.14] Release 1.0 (final)
-- Bugfixes
[05.05.12] Release 0.2
-- implements polyalphabeticel substitution