In Vanilla World of Warcraft, abilities activate when you release a key. The ClassicSnowfall addon makes it so abilities activate as soon as you press the key. It's a small, but important, difference that makes every action just a little bit more responsive. Everyone should have this installed. In later versions of World of Warcraft this was built into the client itself.
For many more useful addons, check out my Vanilla World of Warcraft Addon Guide.
You can download ClassicSnowfall from:
Extract the downloaded file and drag the ClassicSnowfall folder into the Interface/AddOns folder in your World of Warcraft game folder.
How to Use
Just install the addon and it automatically works. There is only one available option, the ALT self-cast feature. By holding down the ALT key and activating an ability, it will cast on yourself. This is disabled by default. I have never found the need to use this, but the option is there if you need it.
|/csselfcast||Toggles the ALT self-cast feature. (Default is off.)|