I always use this library for myself, and I personaly think that is VERY usefull. Its clear that Arduino doesen't support real parallel processes, but we can "sort" of do it with scheduled tasks.
Yes, there is already an class called "Scheduller", but for big projects (likes the ones I do, with more than 15.000 lines), it's not "good" enought...
I LOVE Object Oriented stuff, and this follows it pretty much.
Check out the library here: https://github.com/ivanseidel/ArduinoThread
It also works for ANY arduino, but I implemented thinking on the DUE, since it's capable of more stuff (I use it with my ArduinOS, and it's just perfect =] )
Any suggestions are welcome!