Identify which features are present in Slack: Set C

Zulip

"Help us prepare the comparison page between Zulip and other chat tools, with a matrix of which features each product has or doesn't have. Your task is to test Slack and figure out which all features are present in it. See https://github.com/zulip/zulip-gci/blob/master/tasks/chat-application-comparison.md#set-c to see the features you have to test and the output format.