WireMock is described as 'simulator for HTTP-based APIs. Some might consider it a service virtualization tool or a mock server' and is an app. There are more than 10 alternatives to WireMock for a variety of platforms, including Online / Web-based, Mac, Windows, Linux and SaaS. The best alternative is Beeceptor, which is free. Other great apps like WireMock are Mockoon, Mockintosh, SOAP/REST Mock Service and QuickMocker.
SOAP/REST Mock Service is a simple configurable framework to mock out SOAP or RESTful (or "REST-like") webservices. It's main goal is to support automated integration testing of applications that integrate with 3rd party webservices.
Online API Mocking Tool: API Mock, fake API, stub API, simulate API, dummy API. Capture and debug requests instantly. Forward requests to localhost for webhooks testing and debugging. More than 100 random or faker shortcodes for response templating.
SmartMock.io is a tool to set up, manage, and troubleshoot HTTP protocol API mocks (REST, SOAP, JSON-RPC) in the cloud. This frees you up to focus on the logic of your mocks and not have to think about boilerplate code of your own HTTP mock servers.