Today on August 1st at 4 AM (UTC), what many have described as an "altcoin" will fork off from the main Bitcoin network. August 1st is also the scheduled activation of BIP 148, also known as the User Activated Soft Fork (UASF).
The new, forking coin, called "Bitcoin Cash", will launch as a so called User Activated Hard Fork (UAHF) but in reality it's a Miner Activated Hard Fork. All Bitcoin (BTC) holders will receive an amount in Bitcoin cash equivalent their Bitcoin holdings. 1 for 1.
Here is a graph I have created that shows which Exchanges currently will support "Bitcoin Cash" or not support it, and which Exchanges will start trading "Bitcoin Cash" from today.
(Images sourced from Google images)