Ace was created because many different mods have to use the same types of basic functions. With ordinary mods, these basic functions would be written and included with each addon. With Ace, this basic functionality is packaged into a single library that all Ace mods use. What this means to non-programmers is that Ace mods use fewer system resources, because they all use a the standard Ace code, which is loaded once for all of the Ace mods you have. If you're using non-Ace mods, these basic functions are loaded seperately for each addon you have -- and the more addons you have, the more this adds up. (On the flip side of this, if you only use one Ace addon, you don't gain any benefits, but if you use all Ace addons, a little efficiency improvement in each can result in a big difference.) For the programmers in the audience, Ace means you can write your addon quickly, because you have immediate access to basic Ace functionality (you don't have to reinvent the wheel -- you only have to write code for what you want to do).
Want to get started with Ace? Read on for a list of some of the best Ace addons out there.
To grab the latest version of any of the addons listed here, go to their page on the WoW Ace wiki (linked below), and click on "Betas" under the link section. Scroll down to the latest download, click, and enjoy!
Decursive: The mod to keep track of all of your decursing needs.
One Bag: Combines your bags into a single convenient inventory display.
One Bank: Combines your bank bags into a single convenient bank display.
SimpleCombatLog: Cleans up the default combat log into something more easily readable.
Elkano's BuffBar: A replacement for Blizzard's default buff display.
Dr. Damage: Calculates approximate damage and healing done by your abilities, based on gear.
FuBar: Same concept as Titan Panel. This is just the base model -- for plugins, you're on your own!
ClosetGnome: Allows you to select different gear setups with a single click.
Cartographer: The only map mod you'll ever need.
oRA2: A CT_RaidAssist alternative.
BigWigs: Boss encounter warnings.
Grid: Raid frames.
Clique: Click-casting mod.
AG UnitFrames: A simple replacement for Blizzard's default unitframes.
PitBull: An advanced, and more customizable replacement for Blizzard's default unitframes.
Omen: The threat-meter of choice.
Chronometer: Ability cooldown tracking.
And for those of you playing on a PC, Ace users can update all of their mods on patch day using the WowAceUpdater application. How's that for convenience!