Protothreads are extremely lightweight stackless threads designed for severely memory constrained systems, such as small embedded systems or wireless sensor network nodes. Protothreads provide linear code execution for event-driven systems implemented in C. Protothreads can be used with or without an underlying operating system to provide blocking event-handlers. Protothreads provide sequential flow of control without complex state machines or full multi-threading.
Use the arduino file directly into you're arduino IDE . And also hex file are available to use for arduino boards and Proteus simulations.
This is a simulation of a led which is blinking during the runtime and user increase it's blinking speed to 4 level by pushing down a button, then the speed will be refreshed. So as it's obvious Arduino is a single core board and it's not able to do multithreading or something like that, but there is a libreary called 'pt' which is related to C language. You can use this library to simulate a program, like it works like multithreading program which it's not :D but it's sounds like one those out there. Enjoy