- [http://requestb.in/](Request Bin) - AKA Postb.in, the original-ish
- [http://bin.mailgun.net](Mailgun's request bin)
- https://www.runscope.com - commercial tool
- http://respondto.it/ - allows mocking of responses
- http://webhookapp.com/ - webhook receiver
- http://httpbin.org/ - Another Runscope util; endpoint/receiver more general HTTP client debugging
- https://ngrok.com/ - native desktop APP which creates public webhook endpoints from behind firewall and allows inspection and replays from local web browser. VERY sweet.
- http://www.zapier.com/ - configurably connect webhooks to other services, including email output.
- http://www.hurl.it/
- APIKitchen
- APIBin
- http://www.getpostman.com/ - Chrome app
- [http://ditchnet.org/httpclient/](Mac HTTPClient) - nice GUI
- https://npmjs.org/package/http-console2 - node CLI / REPL for HTTP requests
- https://github.com/fictivekin/webshell - another HTTP REPL
- ]https://github.com/jbittel/httpry](HTTPry) - sort of specialized tcpdump/ngrep
- [https://chrome.google.com/webstore/detail/dev-http-client/aejoelaoggembcahagimdiliamlcdmfm?hl=en](Dev HTTP Client) - one of many Chrome and Firefox Extensions