...OpenPiano is designed to run entirely locally. It does not require accounts, cloud services, or an internet connection for core functionality.
Project links:
Website: https://www.justagwas.com/projects/openpiano
GitHub: https://github.com/Justagwas/openpiano
Documentation: https://github.com/Justagwas/openpiano/wiki
The application is fully open source. All input handling, playback, and MIDI recording/export are performed on the user's machine.
VirusTotal scan result:
https://www.virustotal.com/gui/file/8e038bb061d4778715006a9d4b0a6ed9b4f5b6565050d5808452316b42eae7d4