Slack has collaborated with Marriott International and Starwood Rooms. You can now compare and book Marriott and Starwood rooms directly through Slack. (This is possible because Marriott and Starwood merged in 2016.)
To do it, you need to add the Marriott Rewards app to Slack. Type /Marriottrewards and the city where you want to book hotel rooms into any Slack channel. You, and everyone else who is in that channel, will be able to see all available rooms and rates.
Not sure how it works? Slack has put together an example of a group of people looking at hotel information and voting on which one to pick. Personally, I found that watching the example made it a lot easier for me to understand how to book a hotel room on Slack. This might be very useful for people who are planning to attend BlizzCon this November.