Yookers

Yookers pens are unusual - fineliners, but filled using standard international fountain pen ink cartridges. The result is a really nice combination - use all sorts of different inks, in a pretty much limitless range of colours, in a pen that's as easy to use as any other fineliner. The porous tips will wear down eventually with use, but they can be replaced as easily as replacing a refill in most other pens.