BitStack is a mobile application launched by a French licensed Crypto-Asset Service Provider (CASP), designed to simplify saving and investing in Bitcoin. Users can link a bank account and automatically round up everyday purchases to the nearest euro, using the difference to buy Bitcoin. They can also set up recurring purchase plans or manually buy/sell small amounts starting from €1. The app includes a non-custodial Bitcoin wallet, allowing users to convert Bitcoin back to euros and withdraw to a bank account at any time, or send it to an external wallet. The platform employs cold storage and multi-signature technology to secure assets, and commits to never using or lending user assets without permission.