Let's you link real names (or whatever you wish) to character names. Then when you see chat from that person the designator you set will be appended to their chat on your client. This does NOT affect anyone else. The addon only modifies chat that is sees on your client. So you don't have to depend on other people to be running an addon like Alias or Incognito or the like in order to see just who is who.

Uncompress the file so that you end up with a LOKWhoIsWho with four files inside. Usually this means you right click it and select Extract Here from the available options. Move the addon into your wow/interface/addons folder. Load WoW and click the Addons button at character select and make sure that LOK_Who Is Who is enabled.

When you log in you'll see a notice in your chat bar (it may scroll out of view) that the addon is loaded. It this is the first time you've logged in a character on this realm with this addon you'll also see a message about trying to load preconfigured data.

At this point the addon is active. The following commands work with the addon from the chat line:

/wiw - Lists commands and options
/wiw enable - turns the addon on and off
/wiw me|mine|own - Turns on/off the showing of your own name
/wiw color red|blue|green|yellow|orange|white|gray|grey - sets the color of the alias.
/wiw reset - wipes out your link database and loads any preconfigured data
/wiw front|rear|back|position|pos - sets the alias to show at the front or back of the chat line or in the case of position/pos will toggle it from front to back or vice versa.
/wiw settings - displays the current settings.

/wiw link CharacterName RealName|blank

The money command. Use this command to link character names to real names or designators of your choice. You could link a character name to person's real name, the name of their main character, their profession, whatever. If you leave off the Real Name portion you will 'unlink' that character and they will no longer have an alias for you. If you want to use spaces in the RealName field then make sure to put quotes '' around it.
Examples:

/wiw link Magilla Steve - When Magilla chats with you you'll see Steve
appended to his chat lines.
/wiw link Pad - will unlink any alias you have set on Pad.
/wiw link Ninjalootah 'This guy is a ninja looter'

Preconfigured Data:

You can preconfigure data for the addon by modifying the LOKWhoIsWho_Config?.lua file in the folder. This is useful for guilds or gaming groups to set up any existing lists of alts+real names before distributing the addon out to their members. You can also send this file out afterwards and use the /wiw reset command on each client to load the pre-configured data. This will wipe out any custom changes the client may have made though so be warned.

--Acknowledgments to code and ideas from the following addons

--TimeStamp by Andreas
--InfiniteIgnore by BlueDragon
--CastParty by Hanboo
--And me of course bastardizing everything I come in contact with.