This is a serverless app that can be linked to SlackBot.
On a fixed day of the week at a fixed time, this app draws 3 groups of 3 people from Slack. So we have drawn 9 people, which are unique and do not repeat. A group is a conversation of 3 people. It is not a channel. The bot adds a meme to each group (webservice with memes with API access) and starts a conversation by sending some messages.
Application runs as a spring cloud function and it is deployed on AWS Lambda. The trigger is set by Amazon EventBridge Rule (more info: here).
Environment variable SLACKBOT_SERVICE_URL should be set to point to above mentioned SlackBot api.