List of available user-contributed function packages
Gretl has a very nice "function package" mechanism (in GUI go to: File -> Function Files -> On server)
Users can make their function packages available to the Gretl community by uploading them to a public server from within the Gretl program. Downloading those packages from within Gretl is even simpler, and executing a package presents a dialog window for easy parameter input. (Command-line execution or usage in scripts is of course also possible.) For more details, see section 10.6 of the Gretl manual and the section How to contribute user packages and functions in this wiki.