Password Composer is described as 'Generate a different, safe password for every site you register with. You only need to invent and remember one strong Master Password' and is a Password Manager in the Security & Privacy category. There are four alternatives to Password Composer for a variety of platforms, including Mac, Windows, Online / Web-based, Android and iPhone. The best alternative is 1Password. It's not free, so if you're looking for a free alternative, you could try Keychain Access or Secure password generator (twice secure).
1Password creates strong, unique passwords for all of your sites and logs you in with a single tap (or click). A single click opens your browser, opens a site, fills in your username and password, and logs you in.