Whetstones
Aka wet-stones
Wet Stones are my preferred way to keep my kitchen knives sharp. The only other method I find attractive is the rolling tumbler that have recently hit the market. Still I think wet stone is more adaptable and reenforces the mindfullness surrounding my knife hobby.
When I bought my first Japanese knife I also grabbed this cheap amazon wetstone "DDF IohEF" . After a half a year of using it I've noticed the surface has become quite uneven. Working on solving that now see [[Whetstone Flattening]]. Besides that I'm keeping my eye out for a better wet stone. This page contains my research on that.
Dieter Schmid
Really nice article from Dieter Schmid covering picking stones at: https://www.fine-tools.com/japwas.html
thechefdojo guide
This article breaks down some nice Japanese Whetstone brands.
Beginner: KING 1000 / 6000
Intermediate: Shapton Pro / Kuromaku 1000
44 EUR on amazon
Stone Pond
Really cool all in one solution to holding, storing, and using stones. Also includes a glass plate with laminate to help flatten stones (lapping). Seems it is targeted at work worker sharpening tasks but should also work for knife sharpening. https://www.fine-tools.com/schaerfstand.html
71 EUR