This is an action button modification addon. Its primary purpose is to improve the visual status indications that the action buttons provide.
Cooldowns
The Blizzard UI shows cooldowns for abilities on action buttons, and these cooldowns are a combination of the true ability cooldown, the global cooldown, and power cooldowns (for abilities that use runes). This addon removes the display of global cooldown and power cooldown so that you see just the true ability cooldown. This is much more informative and less distracting than having the same global cooldown and power cooldown information repeated on every button. You will still want to have a global cooldown indicator somewhere in your UI, so make sure that you have a separate addon installed that displays the global cooldown (like Quartz or SnowfallRune).
Fading
The Blizzard UI fades action buttons when you do not have enough power (mana, rage, focus, energy, happiness, runes, or runic power) to activate the associated ability. This addon can disable the fading for any power types you choose (by default, only runes). This feature is particularly useful for runes, which would in the Blizzard UI cause your action buttons to fade/unfade very frequently, which is quite distracting and unhelpful. Do not use this feature with another addon's action button range indicator, because this feature will be overridden by the other addon and then be ineffectual. Instead, use the SnowfallActionButton range indicator.
Range indication
This addon shows a red overlay over an action button when the target is out of range. The red overlay will appear over the whole button whenever the action button hotkey text is red, so make sure that you haven't disabled the hotkey text color changing using some other addon.
Configuration
There is no in-game configuration. In order to configure the addon, copy the "Interface\Addons\SnowfallActionButton\SnowfallActionButtonSettings" folder and paste it at the "Interface\Addons" level. Congratulations, you have just created your very own addon called "SnowfallActionButtonSettings". Now edit the settings in "Interface\Addons\SnowfallActionButtonSettings\SnowfallActionButtonSettings.lua" to your liking. There are details on what each setting does inside that file.