RGB Protocol (v0.11.1) does exactly what you ask: fungible assets on Bitcoin and Lightning without using a sidechain or trusting a federation. It has been live on Bitcoin mainnet since July 2025.
Instead of a separate chain, RGB uses client-side validation: asset data is kept entirely off-chain and exchanged directly between the parties involved.
Only a compact cryptographic commitment is anchored inside a Bitcoin transaction, via an OP_RETURN output (Opret) or an unspendable script leaf in the taproot taptree (Tapret). Bitcoin remains the settlement and anti-double-spending layer; no additional trust is introduced.
For asset types, RGB defines schemas, i.e. declarative contract templates. The main ones for fungible tokens are:
- NIA (Non-Inflatable Asset) — fixed supply
- IFA (Inflatable Fungible Asset) — with secondary issuance up to a defined cap
Both issue assets whose ownership is tied to Bitcoin UTXOs via single-use seals, and both work natively over Lightning Network channels without any changes to the Lightning protocol.
Full documentation: docs.rgb.info
Disclosure: I work for the RGB Protocol Association (rgb.info), the organization supporting RGB Protocol v0.11.1.