The Slack bot is related to the Slack app, a real-time messaging, archiving and search tool for modern teams. Yet it wasn't created by Slack. Instead, Lydia, a French payment app, created the Slack bot. Why? It saw the need for Slack users to settle account balances and decided the best way was through a simple monitoring of at-mentions.
Tech Crunch illustrates, "For instance, you could say “I hope you enjoyed the burgers. @jordan @matt you owe me €10 each. cc @lydia.” Then, Jordan and Matt receive a notification on their phones asking them to confirm the payment. They can review and accept and you get back your €20." The Slack bot is one example of how apps can and will be cross-pollinating.