Located in alphabetical order (not prefer)

• ab – slow and single threaded, written in C

• wrk – multithreaded, but doesn't offer concurrent connections and a keepalive switch, written in C/Lua

• wrk2 – constant throughput, correct latency recording variant of wrk, written in C/Lua

    Concurrent connections are enabled with:
      -c, --connections <N>  Connections to keep open
    And keepalive (which is default) can be disabled using:
      -H "Connection: close"
  

• apib – most of the features of ApacheBench (ab), also designed as a more modern replacement, written in C

• baloo – Expressive end-to-end HTTP API testing made easy, written in Go (golang)

• baton – HTTP load testing, written in Go (golang)

• bombardier – Fast crossplatform HTTP benchmarking tool, written in Go (golang)

• curl-loader – performance loading of various application services and traffic generation, written in C

• drill – Drill is a HTTP load testing application inspired by Ansible syntax, written in Rust

• fasthttploader – benchmark (kinda ab) with autoadjustment and charts based on fasthttp library, write in Go (golang)

• fbender – A load-testing command line tool for generic network protocols (HTTP, DNS, DHCP, …), written in Go (golang)

• fortio – load testing library and command line tool and web UI. Allows to specify a set query-per-second load and record latency histograms and other useful stats, write in Go (golang)

• gatling – High performance load testing framework based on Scala, Akka and Netty, write in Scala

• go-wrk – a HTTP benchmarking tool based in spirit on the excellent wrk tool (wg/wrk), write in Go (golang)

• goad – Goad is an AWS Lambda powered, highly distributed, load testing tool, write in Go (golang)

• gobench – HTTP/HTTPS load testing and benchmarking tool, write in Go (golang)

• gohttpbench – ab-like benchmark tool run on multi-core cpu, write in Go (golang)

• hey – HTTP(S) load generator, ApacheBench (ab) replacement, formerly known as rakyll/boom, written in Go (golang)

• htstress – multithreading high-load bechmarking services (>5K rps), written in C/Linux

• httperf – difficult configuration, slow and single threaded, written in C

• inundator – A simple and high-throughput HTTP flood program, written in C/Linux

• jmeter – Apache JMeter™, pure application designed to load test performance both on static and dynamic resources, written in Java

• k6 - A modern load testing tool scriptable in ES6 JS with support for HTTP/1.1, HTTP/2.0 and WebSocket, written in Go (golang)

• locust – easy-to-use, distributed load testing tool with real-time web UI. Simulates a swarm of concurrent users, the behavior of each of them is defined by your python code. Written in Python

• mgun – A modern tool for load testing HTTP servers, written in Go (golang)

• pounce – evented, but results fluctuate, it's sometimes faster than htstress, written in C

• siege – slow and single threaded, written in C

• slapper – Simple load testing tool with real-time updated histogram of request timings, written in Go (golang)

• slow_cooker – A load tester focused on lifecycle issues and long-running tests, service with a predictable load and concurrency level for a long period of time, written in Go (golang)

• sniper – powerful & high-performance http load tester, written in Go (golang)

• tsung – Simulate stress users in order to test the scalability and performance of IP based client/server applications HTTP, WebDAV, SOAP, PostgreSQL, MySQL, LDAP and Jabber/XMPP servers, written in Erlang

• vegeta – HTTP load testing tool and library, written in Go (golang)

• weighttp – multithreaded, but slower than htstress without keepalive, written in C

• welle – ab (Apache Benchmark) like tool, written in (Rust)

• Multi-Mechanize | Performance Test Framework
• Performance test tools list
• REST API client - simple, beautiful, and free REST API client (Mac, Windows, and Linux)