Inn4Wallet is a cryptocurrency wallet with a portfolio of more than 100 assets. With it, all traders have the opportunity to compare currencies to Euro or US Dollar equivalent. Though, Inn4Wallet is not just a wallet, but also a platform that can be connected to any third-party services through the API for the comfortable purchase or sale of cryptocurrencies, including transactions using a bank card.The challenge The key requirement for our team was to create an application that will support 9 major cryptocurrencies at the MVP stage. These currencies, among others, are: BTC, BTC CASH, DOGE, ETH, EOS, LITECOIN, RIPPLE, STELLAR, DASH. Another challenge that the application should have proper security (login via PIN, password, fingerprint, iris scanning), taking into account the possibility of sensitive data backup (seed and backup phrases/private keys). Key requirements to the system: Storage of the top 100 cryptocurrency portfolio and displaying the cryptocurrency equivalent in fiat (USD, EUR, etc., selected by the user). Supporting all major cryptocurrencies (top 100), ERC20, ERC-223, ERC-721 tokens. Supporting all tokens and forks of the following currencies: BTC, BCH, ETH, ETC, LTC, DASH, XRP, XLM, EOS, TRX, USDC (token) and more. Connecting third-party services for the purchase and exchange of cryptocurrencies, verification or replenishment of a mobile phone, etc. upon the wallet interface. Opportunity to expand the exchange functionality - connecting a third-party exchange service and the ability to give the user a choice of changing ways (for example, displaying rates of each exchange - sorting by rates - and let the client decide where to change). Receiving and sending cryptocurrency without restrictions to any supported address. What we did Our team has created the application’s backend and frontend as well as its mobile versions for iOS and Android. The whole system was implemented according to the principle of micro-service architecture, which allows not to interfere with the work of other services in case of possible problems with one service. We have also developed a separate monitoring system. This is special monitoring, signaling and reporting service for tracking emergency situations and use cases within the system. The result As a result, we were able to implement a high-load application, with a portfolio of major cryptocurrencies (such as BTC, BTC CASH, DOGE, ETH, EOS, LITECOIN, RIPPLE, STELLAR, DASH). The application has an intuitive, native interface, so even beginners who only are learning the cryptocurrency world can easily figure out how to manage crypto assets. Inn4Wallet also boasts its security in terms of storing sensitive data. Therefore, crypto enthusiasts can be sure of the safety measures taken to keep their assets.