(All our assumptions were wrong)
I'll be talking about all the things we got wrong bringing DayBack Calendar to the Salesforce App Exchange. (http://sforce.co/1SlhFuE) This will be mostly non-technical--assumptions about culture, audience, and platform--but if the audience is interested we can get into some of the technical differences in how FileMaker concepts translate to Salesforce.
If you're interested in how a JS app like DayBack actually runs in Salesforce, there is something similar to a "webviewer" in Salesforce. It's called "canvas" and here is Jason Young's Dreamforce '16 presentation on why canvas apps rock: https://dayback.com/dreamforce-2016/