What is Savi and why does it exist?
Please see this blog article that explains the motivation behind Savi.
Overview
Here’s a quick explanation of how Savi is configured.
Installation
To install Savi into your Slack workspace: 
Features
Real-time EC2 events streamed to your Slack Channel(s)
Using light-weight event driven infrastructure, Savi can provide real time updates each time an EC2 instance changes it status - across all your accounts and all your regions.
Share control of EC2 instances via Slack Channel(s)
Let Slack Channel members directly start and stop EC2 instances from Slack.
Savi keeps track of EC2 instances started by a Slack user.
Even if a user forgets to turn off an EC2 instance, Savi will do it for you.
Use tags to track which user started an EC2 instance.
Savi will ensure that the EC2 instances that are started from Slack are properly tagged.
Stop untagged EC2 instances.
Via policy, Savi can shut down EC2 instances that are not properly tagged.