When comparing Mou vs Quiver, the Slant community recommends Mou for most people. In the question“What are the best Markdown editors for OS X?” Mou is ranked 8th while Quiver is ranked 16th. The most important reason people chose Mou is:
Mou has word auto-completion (accessed via 'esc') for English words, text transformation such as conversions to uppercase, blockquote or an h1 heading, HTML entities (such as <’s, &’s and spaces) that can be added anywhere in the text and customizable keyboard shortcuts for everything allowing for efficient use of the software's capabilities.
Specs
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Pros
Pro Advanced text editing
Mou has word auto-completion (accessed via 'esc') for English words, text transformation such as conversions to uppercase, blockquote or an h1 heading, HTML entities (such as <’s, &’s and spaces) that can be added anywhere in the text and customizable keyboard shortcuts for everything allowing for efficient use of the software's capabilities.
Pro Full syntax highlighting
Mou provides full syntax highlighting for Markdown. The highlighting can be customized manually or by applying a predefined theme.
Pro Has real-time split-screen preview
Mou is split into two columns. It displays raw Markdown on the left and formatted text on the right. Text on the right will update in near real-time as raw Markdown is written.
Pro Powerful search
Mou can do incremental ("find as you type") pattern matching search. For example, it can find all words that have x as the third letter followed by at least 4 more letters and a line break.
Pro Free beta versions
Mou is available as a free download up until the release of 1.0.
Pro Customizable
The whole editor can be customized using different color schemes and users can create own variations by editing CSS.
Pro Support for CJK characters
Mou supports CJK characters for writing Markdown in Chinese, Japanese or Korean.
Pro Export as HTML or PDF
Markdown can be exported as an HTML or a PDF file. Each export can also be styled by a custom CSS.
Pro Customizable keyboard shortcuts
Mou has keyboard shortcuts for all text manipulation actions allowing for highly efficient use of the software. These shortcuts can also be manually edited to better fit each individual workflow.
Pro Includes optional typewriter keypress sounds
The app includes optional atmospheric typewriter sounds that are triggered with each keypress. These can be enabled in the settings.
Pro Scriptogr.am & Tumblr integration via Dropbox
Mou allows writing and publishing to blogs from within the editor.
Pro Has more features than just a simple Markdown editor
Quiver is a notebook and note-taking app akin to Evernote which happens to also be able to edit Markdown files. As such, it has a lot of useful features such as: image support, file attachments, web content support and more.
Pro Supports code highlighting
Has syntax highlighting for more than 120 programming languages.
Pro Notes can be linked to each-other
Quiver notes have unique links that can be copied and pasted into other notes to gain quick access between them.
Pro Live preview
Quiver has live preview for both Markdown and LaTeX. This helps users to better understand the way they are formatting their files.
Pro Cloud syncing
Dropbox, iCloud Drive, Google Drive, or any other file-based cloud services.
Pro Supports vi keybindings
For people used to vi keybindings, Quiver can be set up to work with them.
Pro Combination of different types of writing in one note
The most outstanding thing for me. Use HTML line breaks while writing MD text.
Also, unlike most hybrid editors like Bear, it supports instant image sizing and respective preview.
Cons
Con No longer maintained
The latest version was released in 2014, version 1.0 was announced for 2015 but was never released. The app is not compatible with macOS Sierra.
Con Only free until 1.0 release
Once 1.0 is released (still unreleased as of May 2017, release was planned for August 2015), Mou will cost $30. It can currently be pre-ordered for half the price.
Con Text is hard to read on a big screen in full-screen mode
On big screens legibility is pretty bad when entering full-screen mode because the text is not columned nor centered. On smaller screens though, legibility is quite good even on full-screen.
Con Doesn't work as well with non-monospaced fonts
When using a non-monospaced font, the text jiggles around. It can be very annoying since users may not always want to write with a monospaced font.
Con Switching live preview on/off changes the width of text area
Con v1.0 was promised to Indiegogo founders more than a year ago
Safe to say this is dead software at this point.
Con You can't edit specific files, they must be in your notebook
Con No iOS apps for editing, only a viewer available
I'd LOVE to edit and create quiver notes on my iPad!
Con The line in focus shows a border around it which is distracting
The line in focus in the editor shows a rounded rectangular border around it, which is unappealing and distracting.
Con Much more than a simple Markdown editor
Since it's more like a note-taking app (and a note-taking app built for developers) than a Markdown editor, it may be a little excessive to use it only for its Markdown editing features.