The 'boy scout' rope twister works pretty well.
there is also a jig that you can make with three hooks, attached to a handle, which you turn to twist the rope. The scout jigs are easier to build but the other is turns a tighter rope more easily.
I will get some pics put up in the next day or two, to see how it is built.
You can also twist rope starting with sigle strand, twisting and doubling back on self. You can keep twisting and doubling until desired thickness.
Which method I use depends on what size and kind of rope I want and where I am at.
For the best quality, tightest and longest ropes, I use my rope jig... For a quick job or teaching scouts, I will often use a jig like the above posted pics. If I just need something small or if I am in the hills, I usually just twist the strands.
My brother's and I were up in the mountains some time ago and decided to go fishing. We twisted yucca into line, whittled some stick hooks, cought some bugs, then were off fishing. We had brown trout for dinner.
I have also twisted fibers into long double stranded strands and then used either of the above jigs to twist them into three standed rope.