Renamed to davidboers/ElmEither. That is where the repository lives now. It has not been published as a package under the new name.
Versions published as kingwither/elmeither still install under that name. 1 version of 1 come from the new location (see their notes).
Rerouted (renamed, verified). The GitHub user or repository was renamed. The tag is still there, at the new name. The Lamdera package server serves a copy recovered from https://github.com/davidboers/ElmEither.
What we checked: The repo moved to github.com/davidboers/ElmEither and tag 1.0.0 is there; its commit 3daeeb6718bb is from 2021-05-07 18:31 UTC, before the version was published (2021-05-07 18:33 UTC); elm.json is byte-identical to package.elm-lang.org's; the exposed modules match docs.json; the zip's SHA-1 is not the published one (GitHub's zip no longer comes out byte for byte the same), so the contents were checked instead.
The Lamdera compiler uses this copy and prints a one-line notice saying so. elm itself fails to download this version.
Details · package.elm-lang.org's zip: https://github.com/kingwither/elmeither/zipball/1.0.0/
Haskell's 'Either' type
elm install kingwither/elmeitherPublished on 7 May 2021 under the BSD-3-Clause license.
Elm version 0.19.0 <= v < 0.20.0
Rerouted (renamed, verified): the zip served is the recovered copy, SHA-1 d9fd5a51ec80e564efddd02f41a19712084566b2.
Files: elm.json · docs.json · endpoint.json · README.md · releases.json