Fiddler, web debugging proxy.

Nginx plus, Application Platform.

Membrane Service Proxy, Open Source API Gateway & HTTP reverse proxy for REST & SOAP.

Pushpin, Drop-in proxy server that pins client connections open, making realtime push easy.

REPOSE, solutions to API processing tasks such as authentication, rate limiting, API validation, HTTP Request logging, and much more. It is an open-source RESTful middleware platform that is highly scalable and extensible.

Envoy, edge and service proxy, designed for cloud-native applications.

HAProxy, a solution offering high availability, load balancing, and proxying for TCP and HTTP-based applications.

Apache JMeter, designed to load test functional behavior and measure performance. It can be used to simulate a heavy load on a server, group of servers, network or object to test its strength or to analyze overall performance under different load types.

Runscope, cloud service for API Monitoring.

mitmproxy, a proxy for debugging, testing, privacy measurements, and penetration testing. It can be used to intercept, inspect, modify and replay web traffic such as HTTP/1, HTTP/2, WebSockets, or any other SSL/TLS-protected protocols.

Varnish Cache, a web application accelerator. It acts as a web application accelerator focusing on optimizing caching and compression.

HAProxy, a load balancer and proxy server accelerator. Based load balancing, SSL offloading and performance optimization, compression, and general web routing software.

Squid, a caching proxy for the Web supporting HTTP, HTTPS, FTP, and more. It reduces bandwidth and improves response times by caching and reusing frequently-requested web pages.

Vulcand, a programmatic extendable proxy for microservices and API management.

Traefik, a modern HTTP reverse proxy and load balancer made to deploy microservices with ease.

relayd, load-balancer, application layer gateway, transparent proxy, and SSL/TLS gateway.

Apache Traffic Server, HTTP/1.1 and HTTP/2.0 compliant caching proxy server.

Pound, a reverse proxy, load balancer and HTTPS front-end for Web server(s).