Hey! Johan, co-founder of Castle here. My and my co-founder used to work in a financial startup and couldn't find any easy-to-use solutions for account monitoring. We built Castle to be a drop-in solution against account compromise. You track events in your web and mobile apps, and we analyze device, location and usage patterns to make sure they are consistent for each user.

We have lots of plans for improving the product: more 3rd-party integrations, built-in 2FA/captcha, APIs to build your own "security page" with device and session history. Would love to hear the feedback from the HN community!