If you aren't familiar with Slack, it's a messenger system used by businesses to connect teams and employees (similar to a profession Skype/MSN messenger). Friend of the site Dan Hulton used its API to create a paper and pen RPG - which you can sign up for right here. Slack has apps for PC and Mac, as well as on mobile phones.
Chat & Slash is an old-school hack & slash RPG played using the Slack client with a highly customized bot. It's quite similar to MUDs of old, but controlled via buttons and slash-commands.