WSO2 API Manager - WSO2 API Manager is a 100% open source enterprise-class solution that supports API publishing, lifecycle management, application development, access control, rate limiting and analytics in one cleanly integrated system.
Kong - An open-source management layer for APIs and microservices.
Gravitee.io - Gravitee.io is a flexible, lightweight and an open source API management solution.
Tyk - Tyk is an open-source API gateway and API management platform.
Apigee - Intelligent and complete API platform
API Umbrella - Open source API management platform used by api.data.gov