Hi all,
While seeking some infos on the web about Atlatl/Woomera I found out about another weapon that is halfway between these and the sling.
Since this type of weapon has been mostly found in French archaeological sites, it is called by a French name : Bâton de Commandement, or Perforated Baton.
It is a small sized Atlatl (around 20cm... I let you do the convertion in inches, let's reverse the roles for once, hehe) with a handle and a larger head with a hole in it.
From what I understood, it is not proven that it was used as an atlatl-type weapon... but this guy Ehkahk made a replica with a bit of rope and it does apparently work well.

Ehkahk's version only has a small hole in it... but with a bigger hole like the one below, you can pass the spear through it in order to straighten it easily without using your teeth or legs.

The rope is rolled around the spear, giving it a spinning movement in the air... that might be the reason why Ehkahk says he doesn't need to fletch his spears/darts.
Conclusion : a very light and small weapon, multitool (spear straightener, could be used to make fire as Australian Aborigines did with their hardwood boomerangs, as a head-crusher, shovel, plate or even a bull-roarer), with some multi-purpose string on it too.
No need to bother carrying your spears too as you apparently just need to chop and point a thin trunk or bamboo and there you go !
... I'll definitively try to make one !

And I've also found this text which seems awesome (but in French) : Da Vinci's spear-throwers !

Cheers !

Edit : found out that DavidMorningstar already mentionned it & Paleoarts actually made one :

Please tell us more !

Edit 2 : Loving to combine different utilities in one same object, I've just tied a paracord rope to the handle of my camp knife.
When it's fixed in its sheath, the knife becomes a "bâton de commandement".
Been trying to throw a small diameter pvc pipe with it (only thing approx similar to a spear I had right now).
It works... but no power at all.
I'm guessing the pvc ain't a good spear... and maybe the paracord is too long as well.
In the next days, I'll try with some straight piece of wood and bamboo, and different sizes of cord.

It looks like a reverse mounted amentum on steroids.

Technical explanation of amentum: http://en.wikipedia.org/wiki/Amentum

Pics! http://www.armor.com/amentum.html

David Morningstar has used it before.

The way the cord unwraps around the handle allows the spear to spin, giving extra accuracy. Plus the leverage you get is pretty good.

I'm looking forward to playing around with these, though I'm actually kind of skeptical that they're spear throwers.  There certainly isn't a lot of evidence in the archaeological record to support it, and the vibe I got from the first paper to champion the theory of batons as spear-throwers (Leon Underwood's 1965 paper Le baton de commandement) was that it was a polemic against classifying things as "symbolic" not necessarily proof that it was, in fact, a spearthrower.  And that paper's spearthrowers look wildly different from the swiss arrow model we see today.  That came out in an issue of Primitive Technology in an article penned by Paul Comstock, if I'm not mistaken.  Leon Underwood's initial models presumed significant damage to the artifacts, disguising an atlatl-like hook to propel the darts.

I'm not saying that they're definitely not spearthrowers, the whole thing just reminds me a little bit of this: