Add Notula to the tools directory

_tools/notula.md

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+---
+title: Notula
+category: "documents"
+description: "Notula is a desktop editor for the Markdown in a git repository, with comment threads."
+icon: notula.png
+website: https://notula.org
+syntax:
+  - id: headings
+    available: y
+    notes: "Both the `#` and the underline styles."
+  - id: paragraphs
+    available: y
+  - id: line-breaks
+    available: y
+    notes: "Two trailing spaces and a trailing backslash both produce a line break."
+  - id: bold
+    available: y
+  - id: italic
+    available: y
+  - id: blockquotes
+    available: y
+  - id: ordered-lists
+    available: y
+  - id: unordered-lists
+    available: y
+  - id: code
+    available: y
+    notes: "Indented code blocks are read as code blocks and written back indented."
+  - id: horizontal-rules
+    available: y
+  - id: links
+    available: y
+    notes: "Inline links, reference links, and the `<https://example.com>` and `<name@example.com>` forms."
+  - id: images
+    available: y
+  - id: tables
+    available: y
+    notes: "Edited as a table. The file keeps a pipe table."
+  - id: fenced-code-blocks
+    available: y
+  - id: syntax-highlighting
+    available: y
+    notes: "Provided by [highlight.js](https://highlightjs.org/) and its common language set. A `mermaid` block is drawn as a diagram."
+  - id: footnotes
+    available: y
+  - id: heading-ids
+    available: n
+    notes: "`{#custom-id}` is left in the heading as text."
+  - id: definition-lists
+    available: n
+  - id: strikethrough
+    available: y
+    notes: "`~~two tildes~~` and `~one tilde~`, as in GitHub Flavored Markdown."
+  - id: task-lists
+    available: y
+  - id: emoji-cp
+    available: y
+  - id: emoji-sc
+    available: n
+  - id: highlight
+    available: n
+  - id: subscript
+    available: n
+    notes: "`H~2~O` is read as strikethrough, because a single tilde is strikethrough in GitHub Flavored Markdown."
+  - id: superscript
+    available: n
+  - id: auto-url-linking
+    available: y
+    notes: "The address is drawn as a link. The file keeps the bare URL that was typed."
+  - id: disabling-auto-url
+    available: y
+    notes: "Put the address in backticks."
+  - id: html
+    available: p
+    notes: "HTML is kept in the file exactly as written, and shown as source rather than rendered."
+see-also:
+  - name: Notula releases and release notes
+    link: https://github.com/anetrebskii/notula-releases/releases
+---
+
+[Notula](https://notula.org) is a desktop editor for the Markdown files that already live in a git repository. It opens the repository as a tree of documents instead of a list of files, hides the syntax while you write, and keeps comment threads next to the documents: comment on a passage, reply, mention somebody, resolve. Comments are committed as separate files, so nothing is added to the Markdown itself.
+
+It drives the git already installed on the machine, so a private repository works with the key that is already configured. Every document stays a plain `.md` file that GitHub, Obsidian and Pandoc read, and blocks nobody edited are written back byte for byte, which matters if the files are reviewed in pull requests.
+
+Notula is free, and it runs on macOS and Windows. There is no Linux build yet and no browser version. The source is closed, and the builds are not code-signed, so the first launch takes an extra step on each platform.
+
+{% include image.html file="/assets/images/tools/notula.png" alt="Notula editor interface" width="80" %}
+
+Notula parses CommonMark with the GitHub Flavored Markdown extensions, plus YAML front matter, which it shows as editable fields at the top of the document. Two consequences show up in the table below. A single tilde is strikethrough rather than subscript, so `H~2~O` renders as H<del>2</del>O. And math is recognised between double dollar signs only, which leaves a price in a sentence alone.
+
+{% include tool-syntax-table.html %}