Create an official Slack app
Whilst it is possible to integrate Slack in to Octopus using script steps at the moment, there are now some great possibilities with Slack Apps: https://slackhq.com/get-more-done-with-message-buttons-5fa5b283a59#.uw51h0tvy Steps like manual authorisation steps could be actioned through Slack, each step in a deployment could have an "output result to Slack" option etc.
I would suggest checking out the Microsoft bot framework: https://dev.botframework.com/
It would allow you to integrate with several sources, including slack and teams, from one code base and seamlessly integrate natural language into the interface if desired. We built one recently for our customers and as a .net development shop it was a dream.
Aaron Brown commented
I'd love to be able to interact with octo from within slack. Specifically, i'd like to be able to trigger a deployment via a slack command.
Robert Wagner commented
Great idea and I know there is some enthusiasm for it inside the company. The message buttons are going to be a great help, thanks for the link.