Technically Impossible

Lets look at the weak link in your statement. Anything "Technically Impossible" basically means we haven't figured out how yet.

Markdown note comparison for OneNote user - Joplin, Obsidian and Simplenote


Abstract

Although OneNote has almost all required features, its flexibilities sometime brings inconvenience. Example,

  • tree structure without concept of tagging
  • free area without concept of page
  • formula input with GUI, not notation

This post is exploration of OneNote alternatives and their comparison.

  • Joplin*1
  • Obsidian*2
  • Simplenote*3

They are compared based on following criteria.

  1. can share or sync data regardless of OS or devices.
  2. can input formula.
  3. can tag.

Incidentally, input with markdown is not included in the requirement as a "natural" feature.

Attention: data sharing or sync

Data sync or sharing is commonly described as "sync" in many cases. But it means sharing data on cloud in some cases. This is not data "sync", and it should be described as data sharing. Data sync and sharing is strictly distinguished in this post.

data sync data is stored in device.
data on each devices are synchronized.
data sharing data is stored on cloud.
data on cloud is commonly referred among devices.

Concept or characteristics of application is reflected there.
Example, OneNote saves data on OneDrive, its default location. Although it can save locally, other devices can't refer this data. It means OneNote is data sharing type application.
And Obsidian is data sync type application. It saves data locally, and synchronizes it with assistance of services as FolderSync*4 or GitHub*5.

Summary and comparison

Joplin meets all criteria. Although it offers data sharing as paid service, it allows users to save data online as free.

Obsidian is the runner-up. It is designed to store data locally, and user can't save it online. Although it offers data sync as paid service, plug-in supports data sync at no cost. However, it doesn't always meet demand perfectly. GitHub doesn't support mobile devices, and FolderSync supports only Android. There is no common solution for synchronization.

Feature OneNote Joplin Obsidian Simplenote
substance of data folder
one file
sqlite folder
md file
data sync, sharing sharing sharing sync
sharing
sharing
formula input Math editer TeX notation
MathJax
TeX notation
KaTeX*6
Tagging OK OK
Note Inconvenience from too much flexible Evernote in open source Something unique Account registration required

Joplin

As it supports data import from Evernote, Joplin is as if Evernote in open source. Although data structure is similar with OneNote, it is called differently.

OneNote Joplin
Notebook Notebook
Section Sub-notebook
Page Note
Tag


But data structure on file system is different. All data in Joplin is stored in single sqlite file. Data sharing is possible to save it online.

Export supports retrieving Notebook or Note as a single file. And Browser extension for web clipping is also provided as well as OneNote.

Obsidian

Obsidian has similarities with OneNote and Joplin, but is different in characteristic and impression.

Although Obsidian has same data data structure on application with OneNote, it is called differently. Example, notebook is called Vault in Obsidian.
Data structure on file system is also similar, whereas OneNote handles Section as a single file, Page in Obsidian.


OneNote Obsidian
Notebook Folder Vault Folder
Section one file Folder Folder
Page data in one file Note md file

Obsidian can save Vault online as cloud storage, Obsidian for mobile can't refer them. It provides option to refer local folder as Vault, it doesn't work for for cloud.

Whereas OneNote shows multiple Notebooks in a single window, Obsidian assign window per Vault.

Obsidian is designed to store data locally and offers data sharing as a paid service.

One idea for user driven data synchronization is to make the Vault a GitHub repository. However, Obsidian for mobile can't refer it without trick.

Synchronizing between Vault online and local folder with service as FolderSync, Obsidian can indirectly refer Vault online. And after update local Vault, online Vault can be updated by synchronization again.
But operational consideration is not avoidable. There is the risk as collision between concurrent updates among multiple devices.

simplenote

Simplenote has no advantageous against Joplin and Obsidian. Just list up only some features.

  • account registration is required.
  • only data sharing is provided.
  • data can be exported as JSON and md file.
  • formula input is not supported.