The planet-map generator shown of this page has been developed in small increments over more than 20 years, so the code is a bit messy. But if you just want to run the program, this shouldn't matter for you.
The program runs from a command line, so no fancy GUI. Lots of command-line options, though.
A few examples of maps generated by the program are shown below. Click on the pictures to see larger versions.
The zip file contains the source code (in C), a manual and a few other files. You need a C compiler to compile the program.
The manual is a plain text file describing command-line options and instructions for compiling the program.