When comparing Byword vs ShiftIt, the Slant community recommends Byword for most people. In the question“What are the best power user tools for macOS?” Byword is ranked 33rd while ShiftIt is ranked 46th.
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Pros
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
Pro Easy to configure
ShiftIt is configured through a simple UI where you simply press the hotkeys you wish to map to a certain action.
Pro Free
Pro Intuitive
ShiftIt is very straight-forward to use for most frequent usages.
Pro Open source
Pro Configuration can be committed to your personal dotfiles repository
Configuration winds up living in .hammerspoon/init.lua and .hammerspoon/Spoons/ShiftIt.lua. Very easy to track configuration changes.
Cons
Con No Windows or Linux versions
Con A little slow
Similar to Spectacle, but it has a few more features, such as being able to pick the size adjustment increments. Spectacle was a little faster, though. Repeated size changes or moves in succession can cause it to wait for it to complete.
Con Imprecise when readjusting sizes
Con Doesn't support moving windows between workspaces
There's no way to move a window to a different workspace with hotkeys in ShiftIt.