WSO2 API Manager

WSO2 API Manager is a deeply established, fully open-source platform that is heavily utilized in large-scale government IT systems and international banking. Unlike "freemium" models that limit features, WSO2 releases its entire codebase under the Apache 2.0 license. Organizations only pay WSO2 if they want dedicated enterprise support or managed cloud hosting. Because it was built to handle complex enterprise scenarios, it excels in identity and access management. It integrates seamlessly with existing corporate Active Directory networks and complex OAuth 2.0/OpenID Connect identity providers. It allows banks to comply with stringent "Open Banking" regulations, securely exposing customer financial data to authorized third-party fintech apps via APIs. The platform includes a robust Publisher portal for backend developers to design and deploy APIs, and a highly customizable Developer Portal for frontend developers (or external partners) to discover those APIs, read the documentation, and generate access keys. While its Java-based architecture is heavier than a Golang gateway like Tyk, its comprehensive feature set for regulated industries is hard to match.