BigWigs

Introduction
BigWigs is a boss encounter add-on. It consists of many individual encounter scripts, or boss modules; mini add-ons that are designed to trigger alert messages, timer bars, sounds, and so forth, for one specific raid encounter.

Looking for functionality that BigWigs doesn't cover? Try these addons:

LittleWigs is a plugin for BigWigs and covers all forms of 5 man and solo content.
Capping covers various battleground and world PvP timers.
oRA3 covers all sorts of raid management functionality including raid cooldowns and Battle Res counting.
Old content can be installed by doing a search for BigWigs on CurseForge and installing the appropriate expansion addon.