WinCompse is a free and lightweight application which allows you to type in special characters and symbols in your text. You can easily insert symbols like ♪, ♫, ♬, ∅. Once the application is installed, you just have to press the compose key before you type in the key combination to insert the character or symbol. The Compose Key is the key which enables the key combinations so that the special symbols and characters can be entered.
This software to insert special characters works everywhere starting from Microsoft Word, PowerPoint, Notepad to Windows Live Writer, even in Facebook and browsers.
The best part is that sequence of keys that you need to press to insert those special characters is pretty intuitive, so you will be able to easily remember the key combinations. See screenshot below.
The application is very light weight (less than 1 MB). Once installed, it silently runs in the background and can be accessed anytime from the System Tray in the taskbar. The special symbols can be put in your writings by just hitting the composite key followed by the keyboard key combination. The interesting fact is now you can use these symbols to write files and folder names too.
How to use WinCompose?
Once you download and install the application which is very easy, you will see this 
Before you start writing any document you should know the key combination to get the desired symbols or characters, you will get the list like the one given in the beginning of this article by clicking on the ‘Sequences’ button.
By default, the compose key is ‘Right Alt’, which you can change by clicking on the Compose Key which opens a menu like the one given below.
The Compose Key once pressed lets the key combination to be valid within a time period, which is by default 5 seconds; this can be changed from the ‘Timeout’ button. For example, to type in Æ symbol, we first press the Right Alt followed by Shift+A+E within 5 seconds of pressing the Alt button.
The application contains 1000+ compose rules which can be customized according to your choice; I will let you explore that on your own and won’t cover that here.
Demerit
The application is made only for Windows, it cannot be used in Mac or Linux based operating systems. Secondly you have to remember the key combinations to create a certain symbol (which, though, is pretty intuitive). In case you are trying out a new symbol you have to search in the List of Sequences. You can try other software like KbdKaz 500 and Holdkey which continuously displays what special characters and symbols you are inserting.
Verdict
WinCompose is a great application which can be used anywhere where you would write alphanumeric characters. If you use a few symbols often and can remember their combination, you would love to use it ☺.