When you are writing or editing a document in Office programs like Microsoft Word, OpenOffice Writer, Libre Office Writer etc, you can enter some of the special characters using the toolbar icon to do so. But even these programs do not cover as many characters as the freeware program BabelMap does.
BabelMap is a small portable program that displays a huger number of special characters and symbols. According to the developers, it is able to display the entire repertoire of the unicode characters and contains nearly 137,000 characters. You can browse the characters by choosing a character set from the drop-down list such as Katakana, Khmer or Lao. You can search for the characters by name or by code point. Other than displaying the characters, it also allows you to copy the characters or a string of characters to the clipboard and use it in any unicode ready program such as Notepad++.
Some of the characters might not display on your PC. The reason for this is that you might not have the proper fonts installed in your system for that script. You will have to download and install the unicode fonts that support that character set and then try BabelMap once again. You can change the display font between a single font or a number of fonts (composite fonts). You can find many of the unicode fonts containing a number of character sets from http://unicode.org/resources/fonts.html.
It allows you to bookmark a particular character so that you do not have to find it again. You can just select the bookmark and it will take you to that part of the unicode character set where that character is located. You can add or remove as many bookmarks as you want. You can manage these bookmarks from the toolbar.
You can download BabelMap from http://www.babelstone.co.uk/Software/BabelMap.html.