These days when I've been a bit more busy than usual I thought about warning systems that, without leave WordPress, allow me to communicate with other editors, not forget tasks and things like that.
Well, I started looking and found a few solutions, simple of course. Let's see them, there's something for everyone …
WP Private Messages – Internal messaging system for WordPress. It is a very complete system, with many options and very integrated.
Private reminder – This plugin alerts you when you are viewing a post marked as private. Simple and effective.
Private messages for WordPress – Similar to WP Private Messages, something simpler in its use but just as effective to send messages between the different users of a WordPress.  Pre-Publish reminders – This is one of my favorites. For a collaborative blog, it allows you to leave messages (within the posts) to different editors, such as notices of spelling errors, reminders to add tags or whatever.
Sign out reminder – Simple and effective. Warn registered users that they remember to leave the account before leaving the site.
Post reminder – Are you forgetful? Are there days that you forget to post on your blog? ?, with Post reminder you will receive an email every day reminding you that you have an audience to attend.
Admin post reminder – You already know that it is not convenient to use the administrator user for everything do not?. Well, anyone who plans to enter your WordPress will be very attentive to identify your admin account simply by checking if you write from the administrator account. This plugin alerts you when you are using the admin account at the time of writing posts, so you can use another one less compromised. Curious, is not it?
Category reminder – If you are one of those who forget to assign categories to pots, this plugin is what you are looking for. Stop publishing everything in the default category, rank your blog and let Category reminder remind you of it with a giant balloon of colors.
Old post alert – This plugin is fantastic. Imagine the situation: you come to a blog from the search engines and find a post that seems to solve your problems. But it may happen that you have arrived at an article with old information, perhaps already updated with another entry. Well, Old post alert tells you that you are in an old post and that the information may have already been improved in another publication.
ToDo – You were missing a list of tasks in WordPress ?, since you already have it, install this plugin and you can assign tasks and see them in the Desktop.
Drafts as a to-do list – Do not you want to install a plugin for this? then use the drafts.
Message Ticker – This plugin is a pass, allows you to manage and show notifications to your readers. You prepare the messages and then you can show them, with scroll if you want, in the site of your template that you choose. They are not miniposts, it is something much more immediate and powerful, as well as simple.
User messages – We finish as we started, with another internal messaging system among users, so that your WordPress has capabilities with no need to install a BuddyPress. It is not a system only for the Desktop but it "leaves" your administration area and offers a complete messaging interface in your WordPress. The version 2.0 is for payment but you can download the version 1.2 which is free.