mores

For some reason or other, you might want to allow access to certain posts only to certain people. You can use password-protection on Pages and Posts, but those need to be set individually. 
It’s far simpler to just write a Post, specify a category and all posts in that category are password protected. Or you might decide to protect a lot of old posts. 
Imagine a family blog where certain posts are only visible to people who know the birthday of your first child, or remember your pet’s name. 
Cat-Pass is not for super-sensitive information, it’s for casual use.

Cat-Pass

Cat-Pass lets you password-protect categories. Caution: deactivating the plugin will render your protected posts visible again.

Minor

Simple plugin to secure your WordPress admin interface thanks to IP whitelisting. Only IP addressess on the whitelist (external whitelist supported) have an access into admin interface.
Another possibility how to access WordPress administration is thanks to secret admin link (you still need to insert correct user login and password).
Your IP address is whitelisted and secret admin link generated every time at plugin activation!

Secure Admin IP

Simply restrict login to your WordPress for the specific IP addresses or users with secret link.

Cat-Pass vs Secure Admin IP