Research on the state of online Zettelkasten tool/systems

I am curious about the current state of Zettelkasten [ZK] digital online systems.
Zettelkasten is a form of knowledge management based on linked index cards.

I would like you to spend a few hours (21£ worth) to look at the existing
online tools/systems that implement Zettelkasten, and producing two things:

1. a list of those services/tools with:
- name
- URL of service
- a short description

2. a short analysis of how they compare to each other, if possible identifying dimensions useful for classifying them.


The deliverable is a plain text file organised in the Markdown[MD] format using only the "basic syntax".
URLs should be put in directly without the Markdown link syntax. The file should contain both the list and the analysis.

The work must be delivered by the 26th August 6PM GMT.
The time and monetary constraints are because I have free PPH money that expires after the 26th.

I understand that the output of this sort of work could be a long report or a short email;
my expectations are proportional to the money offered and short notice.
This is more of a test to see wheter I can use PPH for these sort of things and finding people with whom to work.

Thank you for your consideration!

[MD] https://www.markdownguide.org/cheat-sheet
[ZK] https://en.wikipedia.org/wiki/Zettelkasten