DoTimer is a comprehensive suite for managing various things that need timing.  
These include:
    - your DoTs / HoTs
    - your Cooldowns
    - buffs / debuffs on you

It accomplishes the task by breaking into sub-addons: DoTimer, Cooldowns, and PlayerAuras, respectively.  A fourth sub-addon, Notifications, is also included.  All four can be enabled/disabled and customized separately.  The reason for including all of these together in one addon is for interoperability.  You can customize the timers to an extreme extent.  

DoTimer starts off in simple mode, with a lot of functionality hidden.  You don't see PlayerAuras or Notifications, and a lot of the customizability is hidden.  This is for users who have no need of all the complex settings.  

The basic philosophy behind the addon is that timers are put into a specific anchor location on screen.  These anchors can be customized independently of each other, as can the individual timers.  You can control where certain timers from the sub-addons go, so that the timers are placed as logically onscreen as possible.

Fragmentation:
DoTimer's timers fit into three categories: standard, No Target, and Party Buffs.  Standard timers are timers on specific mobs.  No Target timers are timers that can affect multiple mobs at once (or none at all), like Howl of Terror.  Party Buffs are buffs cast on the party; you can set it up so that they get combined into a single timer so that tracking them is much easier (and less spammy onscreen).

Cooldowns's timers fit into two categories: Yours and communicated.  

PlayerAura's timers fit into four categories: Buffs/debuffs with/without a duration.  If you want, you can flag timers that have a duration to display with no duration.

You can customize the anchor location for each of these categories, as well as anchors for specific timers or specific DoTimer targets.  You can also apply timer settings globally, to specific categories, to specific anchors, or to specific timers.  You can make as many anchors and timer settings as you want.

Notifications lets you create notifications for various events, such as casting a spell, an enemy gaining a buff, losing aggro, losing health, or a cooldown being up.  You can make the screen flash various colors, play a sound, send a chat msg / do an emote, or other various things in response.  The system is quite customizable as to how the notifications are sent; I suggest playing around with it.