SwiftDefaultApps is described as 'Replacement for RCDefaultApp, written for macOS Sierra, in Swift 3' and is an app. There are 2 alternatives to SwiftDefaultApps for Mac. The best SwiftDefaultApps alternative is RCDefaultApp, which is free.
RCDefaultApp is a Mac OS X 10.2 or higher preference pane that allows a user to set the default application used for various URL schemes, file extensions, file types, MIME types, and Uniform Type Identifiers (or UTIs; MacOS 10.4 only).
duti is a command-line utility capable of setting default applications for various document types on macOS, using Apple's Uniform Type Identifiers (UTI).
It's the CLI analog to RCDefaultApps and SwiftDefaultApps
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