Whispy

TL;DR

• whispers, regular and bnet
• but in windows, one per person, bubbles
• keeps history, per conversation
• WIM replacement/clone: yes

What it actually is

Whispy is a World of Warcraft addon that pulls whispers out of the chat frame and into proper conversation windows — one window per person, messages laid out as bubbles, and a full history that survives reloads and logouts. Instead of hunting for a whisper that scrolled past three pulls ago, you get a window per conversation that remembers everything that was said in it.

It handles both regular and BattleNet whispers, follows every route the game uses to start a whisper (/w, clicking a name in chat, the unit menu), and stays out of your way in combat.