When comparing Dark Room vs Byword, the Slant community recommends Byword for most people. In the question“What are the best distraction-free word processors?” Byword is ranked 1st while Dark Room is ranked 12th.
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Pros
Pro Portable
As long as the target machine has .NET Framework 2.0 or later installed (and most Windows machines do by default) the software can be run without requiring an install. It can be carried around on an external device, such as a USB thumbstick, and run directly from that.
Pro Decent customization options
Pro Completely free
Pro Word count support
Pro A dark theme is available
Pro Can publish directly to external services
Pro Can export to html, pdf, rtf
In addition to plaintext, Byword can export to HTML, PDF, RTF.
Pro Exemplary Markdown support
Byword de-emphasizes the syntax itself, while emphasizing its effects. It appropriately adds style, like italic and bold, to text that's designated by markdown and dims the syntax so it does not getting in the way of comprehension. Additionally, there are commonly used hotkeys (⌘b, ⌘i, etc) that can be used to apply style without having to know the syntax or having to type it out each time.
Pro Includes features that speed up writing
For example, while authoring a bulleted list hitting return automatically prepares a new bulleted line.
Pro Available for all Apple devices
Byword is available on a Mac, an iPhone and an iPad.
Pro Syncs using iCloud and Dropbox
Documents can be synced using iCloud or Dropbox from within the editor for use across all devices.
Pro Live update support
Cons
Con Requires .NET to be installed
It depends on .NET before it is able to run.