Jython and IronPython are different python implementations, both of which run on different virtual machines. Jython runs on the JVM (Java virtual machine) and IronPython runs on the CLR (common language runtime). This means that programs using these implementations can take advantage of the libraries and ecosystem of the virtual machines. For example, using Jython, I can write a plugin for a Java application, and using IronPython I can use the .NET standard library. The downside to using a different implementation to CPython is that CPython is the most used python, and therefore has the best support from libraries and developers. For example, a popular library like NumPy will only work on CPython, as it relies on CPython's C api, which neither Jython or IronPython can provide.