A pocket-sized fountain pen: small in the pocket and full sized in the hand.

A new pocket pen from Platypus Pens: the Quokka.
Quokka pens are small and cute and turn into full-sized pens when in use. Less than 10 cm long (less than 4 inches), they can slip easily into a pocket or purse and, when posted, they become full-sized pens for writing.

Left to right: Quokka model 10 pattern 1 in onyx and aquamarine; Quokka model 1 pattern 2 in bronze and alpha brass; Quokka model 1 pattern 3 in night sky and aquamarine.
The Quokka pen grip sections are identical to those of the original Platypus Models 1 and 10, so the small size does not come at the cost of writing comfort.
These pictures show the Quokkas alongside a Kaweco Sport, possibly the most popular pocket-sized pen. The Quokkas are shorter than the Sport when closed and slightly longer when posted. The nibs are larger than that of the Sport as well, with a #5 nib in the Quokka Model 1 and a #6 nib in the Quokka Model 10.

Cartridges
The short bodied Quokkas take standard short international ink cartridges like those from Kaweco, Pelikan, Diamine, and others. A huge range of ink colours is available (see those at Jet Pens, Pulp Addiction, or your favourite ink retailer), and empty cartridges can be filled with your favourite bottled inks using a pipette or needle and syringe.
The short cartridges are short, but they fit almost as much ink as an average cartridge converter fill, so you should not worry about running out of ink too often. Anyway, spare cartridges are easier than ink bottles to carry.

Marks and scratches
Pockets and purses can sometimes be fairly rough environments. Pocket pens have to contend with rubbing up against other contents like coins and car keys. The Quokkas are relatively resistant to abrasion as the PLA plastic is fairly hard (harder than, for example, ABS) and the textured surfaces of the pens means that any scratches that do happen will typically be hard to see.
Why ‘quokka’?
The Australian quokka (Setonix brachyurus) is one of the smallest members of the wallaby family, and ‘wallaby’ is what we call smaller species of kangaroo. That means that the quokka is a pocket-sized kangaroo. It’s a marsupial and so the female quokkas have a pocket! What’s more, the other standard name of the quokka is ‘short tailed brush wallaby’ and the Platypus Pens Quokkas certainly have short tails.

The mother quokka (left) has a Platypus Pens Quokka Model 1 in her pocket, and the father (right) has a full-sized Model 10 on his desk. They are discussing when it will be best to give their daughter her first Platypus pen. (She would prefer to have a surfboard.)