It's hard to imagine a modern mobile or web application independent of third-party services (a "third-party source" means a supplier (or service provider). Building a modern application is somewhat reminiscent of building a ship or a rocket when you design a shape, develop control mechanisms and other important functional parts, and then use third-party equipment - add engines, communication and navigation systems, etc. Similarly, to create modern and client-oriented service in digital products, we use integration with various third-party systems, for example, SMS gateway for sending messages or card provider to ensure card issuing and money transfers.
Below is a shortlist of solution providers with which we had to integrate when developing various, mainly FinTech, applications. Perhaps someone from presented providers will be useful for building your product.
Cards, Bank accounts, Checks, Money transfers
Plaid This service provides connection of user's bank accounts to an app. It allows user to see account info, current balance and transaction history as well as transfer money. Works with US, Canada and Europe banks.
Cuallix Credit card issuing, payment processing, various types of loans.
FiCentive Card issuing, card management and various money transfer processing. Brand your card and FiCentive will handle card management.
Payliance Provider with a wide range of payment processing services. Credit and Debit cards payment processing, ACH processing (electronic payments made through the Automated Clearing House (ACH) Network), Payment gateway.
Mitek Mobile check capturing and deposit. Offers various SDK for integration into mobile apps related to mobile capturing (identity verification, documents capturing, automated and accurate data capture).
POS terminals integration
jPOS Open-source, Java, mission-critical enterprise software, based on International Organization for Standardization transaction card originated messages standard (ISO-8583). Allows integrating application with POS.
Messaging, Communication and Support
Twilio We use it as an SMS gateway for text notifications delivering via sms but it's only a small part of their products and services. Twilio offers a wide range of customer notification and engagement tools via various channels (cloud contact centre, text messaging, orchestrated phone calls, emails and so on).
Five9 Omnichannel cloud call centre software (web, video, mobile, social, email, or chat) with IVR and CRM integration. And they have much more inside their solution.
MailChimp and Mandrill Leading and powerful email marketing platform. Group emails or personalised individual emails for clients engagement and notification.
Financial back-end as a service (mainly for e-wallet type of apps)
Coriunder Coriunder is a payment gateway converted into a backend solution giving you tools of a PCI Level 1 processing gateway along with CRM capabilities to manage your employees and your customer billing.
GIACT Fraud detection services for customer identity, account opening and unauthorised payments.
Equifax Provides with FICO scores.
Hopefully, some of these service providers match with your product and will be helpful to you. If you need any consultation about the development of a mobile or web app feels free to contact us. We'll be glad to help you!