Fountain Pens
I’m quite fond of fountain pens, especially when paired with cartridge converters or using a self contained ink filling system. They are both more and less convenient than regular pens. On the one hand they require more care when handling them and cleaning/maintenance. On the other hand, the writing experience feels much better to me, you can load many different types of ink, and (depending on your usage) you could be generating less waste since you don’t have to discard cartridges or entire pens.
Don’t forget different inks interact in a multitude of ways with different kinds of paper, so for the best experience it’s best to evaluate the pen, ink and paper together as a set.