GNU Taler is free software implementing an open protocol. Anybody is welcome to integrate our reference implementation into their applications. Different components of Taler are being made available under different licenses. The Affero GPLv3+ is used for the exchange, the LGPLv3+ is used for reference code demonstrating integration with merchant platforms, and licenses like GPLv3+ are used for wallets and related customer-facing software. We are open for constructive suggestions for maximizing the adoption of this payment platform.
Taler is designed to work on the Internet. To ensure that Taler payments can work with restrictive network setups, Taler uses a RESTful protocol over HTTP or HTTPS. Taler's security does not depend upon the use of HTTPS, but obviously merchants may choose to offer HTTPS for consistency and because it generally is better for privacy compared to HTTP. Taler uses JSON to encode structure data, making it easy to integrate Taler with existing Web applications. Taler's protocol is documented in detail at docs.taler.net.
Taler is currently primarily developed by a research team at Inria and GNUnet. However, contributions from anyone are welcome. Our Git repositories can be cloned using the Git and HTTP access methods against git.taler.net with the name of the respective repository. A list of repositories can be found in our GitWeb.
We have a mailing list for developer discussions. You can subscribe to or read the list archive at http://lists.gnu.org/mailman/listinfo/taler.
The Taler system consists of protocols executed among a number of actors as illustrated in the illustration on the right. Typical transactions involve the following steps: