Nostr client and relay is a Nostr C++ engine that allows to build Nostr applications for command line, desktop or web.
Source code
https://github.com/pedro-vicente/nostr_client_relay
Live demo for the web interface
Programming and API guide
https://pedro-vicente.net/nostr/nostr.html
Workshop demo (Google drive)
https://drive.google.com/file/d/1J7R_RyLRIBAWF-Dqw5sebDhxFUMbCX_N/view