SmartCapsLock

Granted, if you regularly work on the computer, then it is very likely that you started using the Shift key instead of Caps Lock a long time ago. However, unless you deactivate the key, there is always a risk you turn Caps on by mistake and end up writing entire phrases in uppercase.
SmartCapsLock is an application capable of reversing the content in uppercase and hence, spare you the trouble of having to retype everything all over again.

Could use a UI that supports the paste function

After a quick and smooth installation, you can access the application from the System Tray. You should know that the tool does not have an interface per se, but rather a Preferences window from which you can assign combinations of keys for specific actions.
Since the idea behind the app is to save time and energy, it would be nice if the program included an interface that allowed you to paste the text and reverse the erroneous uppercase. Then again, even with this system, you can correct the Caps issue faster than if you were to rewrite the entire content.

Basic functionality that entails assigning hotkeys

It is advisable that you go through the Preferences window and assign keys to the desired actions. You should know that the application does not allow you to use a preference combination of keys. Instead you can use the existing ones to specify the action you want the utility to take. More exactly, you can use reverse case, uppercase, lowercase, capitalized case or do nothing at all.
It is worth mentioning that the app is affected by a limitation of the Windows API, meaning that the clipboard can get cleared when you select the text and press the Caps Lock simultaneously. Since this is related to the functionality of the operating system, there is little that can be done about it.

A tool that can save you some time

While it does come with a few hiccups, SmartCapsLock can come in handy in situations when you need to revise large texts that you accidentally typed in uppercase.