In my opinion casinos take advantage of a loophole in human psychology to take money from people who can't afford it, so having anything to do with that is unethical.
About a year ago WeatherSpark got rid of their very useful dashboard - I particularly liked being able to see a combination of temperature and rain per hour for the next week.
There didn't seem to be an alternative (and there was a Reddit discussion full of people with the same problem) so I started making one.
It took me a year, but it's finally up and has its own domain and everything.
It uses the weather report API from Dark Sky, Google's chart API, free icons from Freepik and the free tier of Google App Engine. About the only thing I'm paying for is the domain name.
Because I'm using the Google chart API I'm limited in how much I can customize how it looks, but it's not too different from what I wanted.
Accurate book recommendations - not what's popular, not something in the same genre as I've read, not by the same author I've read but something I'd actually want to read.
I think the reason this hasn't been done is that (like movies and music) books are so complex that it's hard to tell what someone liked about one book or disliked about another book, so it's hard to know what other books would have that same feature.
Which is why I think ML would be perfect for this - it's good at things like extracting common features, you just has to create one that can read and comprehend novels :)