This is a web-based (zero-knowledge, static client-side only) GUI that wraps the portable implementation of Ed25519 based on the SUPERCOP "ref10" implementation.
https://github.com/GlitchedPolygons/GlitchEd25519
You can encrypt and sign as well as verify + decrypt messages using Ed25519 key-pairs.
Want an .MSI? Download the installer now and use the GlitchEd25519 GUI PWA as an installable standard desktop application instead of relying on your browser of choice.