Simple KOS is a World of Warcraft addon that scans and displays information about players who attack you during World PVP.

Usage:

Simple KOS has two windows: the "Kill On Sight" Window and the "Recent Attackers" Window.

Each window can be moved by holding SHIFT and dragging the window with your left mouse button.
Each window can be closed/hidden by clicking the close button in the top right or by using the slash command.
Each window can be shown again by using the slash command.
Moving your cursor over a player in either window will display additional information about them.

"Recent Attackers" Window - Displays basic information about all players who have attacked you during your current play session.

Left click on a player to copy them to your "Kill On Sight" list.
Right click on a player to remove them from this window.

"Kill On Sight" Window - Displays your PVP enemies!

You can add players to this window by left clicking on them in the "Recent Attackers" window.
If AutoAdd is turned on (see the slash command), then players will be automatically added to this window when they kill you.
Left click on a player to write a note about them. This note will be displayed whenever you move your cursor over the player in the "Kill On Sight" window.
Simple KOS will track your win/loss record against players added to this list. You can see your win/loss record against a player by moving your cursor over them in the "Kill On Sight" window.
Right click on a player to remove them from this window.

Slash Commands - Type /kos in game to see a list of available slash commands.

Note: This is my first addon and it is a WORK IN PROGRESS. Feel free to leave feedback or suggestions and I'll respond as quickly as I can. Thanks!