ON THIS WIKI
The Curse Client is a voice communication program (with the addition of Curse Voice in version 6.0), which has a plugin what allows to control Minecraft modpacks. Minecraft plugin is turned off by default and must be activated from the settings.
All other functionality is pretty the same as in the FTB launcher. You can download modpacks, modify them with other mods available on Curse, download resource packs and maps for map based packs and even create your own modpacks on the base of various Minecraft versions without much effort.
The Client doesn't keep your Mojang account data, all modpacks runs through the official Minecraft launcher that is more preferred by Mojang.
The Client is currently in open beta and available from the Curse Voice website. The current version is 6.2.5575.11267.
The App spotlight from Direwolf20.