NullPass is a password manager that doesn't require you to manage a password file. This is accomplished by combining a single master password with a site specific token (often domain name) to generate a unique password. This password is cryptographically secure and your original password is unrecoverable should an attacker manage to obtain your unique site password. This means an attack on one of the sites you visit will not disclose your password to any other services - keeping your accounts safe.
NullPass does not store any information that you enter, in fact your passwords never even leave your computer! When you enter information into the NullPass form there is some client side code that exectues inside your own browser which does not transmit your information to our servers or the Internet at all.
If you are interested, NullPass works by calculating
SHA-512("length" + "your password" + "domain") and truncating the result to length. You can see this in effect by viewing the source of this webpage, or you can view/fork the project on GitHub!