I have a lot of inside knowledge on how betting odds are calculated as I used to work at a firm that was heavily involved in bookmaking.
I've made a completely free website/tool that predicts the outcome of football games and compares it against the predicted odds that bookmakers worldwide are giving in order to find you the best possible return on bets.
https://cloudbets.io/
It's really just for fun and shouldn't be taken too seriously, but maybe some of you will find the idea interesting!