Air-gapped Bitcoin signers and seed backups from cheap, old or odd hardware. All open source, all early, reviews welcome.

• DTMF-Signer: a signer you build yourself, a Raspberry Pi Pico that hears PSBTs as phone tones and never shows the seed.
• NDS-Signer: air-gapped, stateless PSBT signer for the Nintendo DSi.
• ur-tones: PSBTs and seeds as telephone tones (DTMF), over an audio cable or through the air.
• SeedCraft: back up a seed as a sequence of things (beads, bricks, cards...), readable by software or by hand (demo).

More at github.com/ndssigner.