Billey allows you to keep track of your subscriptions, get notified of upcoming renewals, have a look at spending statistics and much more. Billey has had ~1000 MAU in the last months, and 10k+ users signed up since its publication on app stores about a year ago. Since I introduced IAP ( three months ago ) it has generated ~200 USD per month, with 3-4 purchases per week ( every purchase is a lifetime pro license ). Since it's built with Flutter it can easily run on both Android and iOS from the same exact codebase. The backend is totally serverless ( firebase authentication + firestore + functions + some other gcloud service ) and it has a maintenance cost of nearly zero. Feel free to ask anything by email.