Is there a free Obsidian alternative?

Obsidian is itself free for personal use, so the question is usually about something else — no install, no vault, or working on a machine you cannot install software on. All Markdown covers those and does not try to replace the knowledge base.

Can I open my Obsidian notes here?

Yes. A vault is a folder of ordinary .md files, so drop one in and it opens. Wikilinks and embeds render as literal text, because they are Obsidian's conventions rather than Markdown — which is exactly what they look like to anyone else reading the file.

Does this have backlinks or a graph view?

No, and it is not going to. Those need a vault the tool owns and indexes over time. A page that opens one document cannot build a graph, and pretending otherwise would waste your time.

How do I export an Obsidian note to PDF without Obsidian?

Paste it here and export. Useful when you are on a machine without the app, or when the note has already left the vault. The conversion runs in your browser, so a private note does not go to a service to become a PDF.

Both, most likely. Obsidian for the notes you keep, this for the file someone sent you and the conversion you need once. They do not overlap enough to choose between.

All Markdown vs Obsidian

Obsidian is a free desktop and mobile app that turns a folder of Markdown files into a linked knowledge base, with backlinks, a graph view and a large plugin ecosystem.

All Markdown compared with Obsidian
	All Markdown	Obsidian
Cost	Free	Free for personal use; paid for commercial and for sync
Installation	None — open a tab	Desktop and mobile apps
What it is for	One document at a time	A vault of linked notes, built over years
Backlinks and graph	Not supported	The main reason to use it
File system access	Open and download files; no folder access	Owns a folder, edits files in place
Syntax	Standard Markdown and GitHub Flavored	Standard plus wikilinks, embeds, callouts and highlights
Plugins	None	A large community ecosystem
Convert to PDF or Word	Built in, both directions	PDF export built in; the rest needs plugins
Works on a locked-down or borrowed machine	Yes	Only where you can install software

Open the editor

Obsidian and All Markdown get compared because both are private, both are free to start with, and both work on plain .md files. They are answers to different questions.

Obsidian answers where do my notes live. It takes a folder, indexes it, and gives you backlinks, tags and search across everything you have ever written. That is a commitment measured in years, and it is worth making.

All Markdown answers what do I do with this file. Someone sends you a README, you need a note as a PDF, a .docx has to become Markdown. One document, one job, no vault.

What Obsidian does better

Obsidian is a knowledge base, not an editor. Backlinks, tags, the graph view and search across a whole vault are the reason to use it, and none of them mean anything to a tool that opens one document at a time.
It owns a folder on your disk. Files stay where you put them, sync through whatever you already use, and are still there if Obsidian disappears tomorrow — which is a stronger guarantee than any browser tab can make.
The plugin ecosystem covers things no browser tool will ever ship: Zotero citations, Dataview queries, canvas boards, spaced repetition, Git versioning of the vault.
It works fully offline as a real application, including on mobile, with no dependence on a page being reachable.

What All Markdown does better

Nothing to install, which matters on a machine you do not administer — a work laptop, a Chromebook, a borrowed desktop.
It converts in both directions on the spot. A .docx, a PDF, a spreadsheet's clipboard or a web page becomes Markdown here; Markdown becomes PDF, Word or standalone HTML. Obsidian needs a plugin or an export for most of that.
Obsidian's own syntax does not travel. Wikilinks, embeds and highlights are its conventions, and this renders standard Markdown — which is how you find out what a note looks like to everyone else.
For one file, it is faster. Opening a vault to read a Markdown someone sent you is a lot of application for the job.

Which to choose

These are not really competitors. Obsidian is where you keep notes for years, and if that is what you want, use it — nothing here replaces backlinks or a vault. All Markdown is the tab you open when someone sends you an .md file, when you need one note as a PDF on a machine without Obsidian, or when you want to see what a note written with wikilinks actually looks like to a reader who does not have them. Most Obsidian users want both, and neither costs anything.

Common questions

Is there a free Obsidian alternative?: Obsidian is itself free for personal use, so the question is usually about something else — no install, no vault, or working on a machine you cannot install software on. All Markdown covers those and does not try to replace the knowledge base.
Can I open my Obsidian notes here?: Yes. A vault is a folder of ordinary .md files, so drop one in and it opens. Wikilinks and embeds render as literal text, because they are Obsidian's conventions rather than Markdown — which is exactly what they look like to anyone else reading the file.
Does this have backlinks or a graph view?: No, and it is not going to. Those need a vault the tool owns and indexes over time. A page that opens one document cannot build a graph, and pretending otherwise would waste your time.
How do I export an Obsidian note to PDF without Obsidian?: Paste it here and export. Useful when you are on a machine without the app, or when the note has already left the vault. The conversion runs in your browser, so a private note does not go to a service to become a PDF.
Which should I use?: Both, most likely. Obsidian for the notes you keep, this for the file someone sent you and the conversion you need once. They do not overlap enough to choose between.

Written from public information about Obsidian and from using it. Features change; if something here is out of date, the other project's own documentation is the authority, not this page.