Multi-step forms, without a gem?

I am looking for a good way to get multistep forms working, I have seen a couple of ways to do this and each has their own merits.

Now I would like to be able to navigate back and forth between the steps, so saving the state maybe needed. I am not sure if to save at each step, and say x step was not complete the next time the log in, or make them start again.

So any input would be awesome from those who have tackled the multi-step journey.

Thanks
Alan