Stand Alone, Inc. - Protektor

Protektor	Price: $29.95
Keep your applications safe, with Protektor!
Protect your applications with Protektor. Protektor lets you assign a password to any of the applications on your Newton, so only you can access them. You can even put a password on Protektor itself, to make sure that nobody can change your passwords.
You can enter passwords through one of two different keyboards. One is just for numbers.
The other is for letters, or a combination of letters or numbers.

Download for Newton 2.0 Compatible Devices