What is the best way of integrating Rulai with any existing apps?

If you have access to the fitness app's code, there are several options: 1) You can have a button that leads to a webview for the bot. In this case, you would be using our widget (which is customizable). 2) You can create your own front-end chat client, and use Rulai's Dialog API to send and receive messages to and from the bot. 3) If the app allows it, you can embed the 2-liner HTML snippet into the code's front-end, so there wouldn't be a webview. This would be using Rulai's widget.