From the Stellar FAQ[1]: "Lumens are the native asset of the Stellar network.
Native means that lumens are built into the network. Asset is how the network refers to an item of value that is stored on the ledger.
One lumen is a unit of digital currency, like a bitcoin.
While you can’t hold a lumen in your hand, they are essential to the Stellar network—they contribute to the ability to move money around the world and to conduct transactions between different currencies quickly and securely."
After reading up on Taler, it sounds like a very similar idea to Stellar, but Stellar removes some of the need for trusted authorities.
From the Taler overview: "The system requires an external auditor, such as a government-appointed financial regulatory body, to frequently verify the exchange's databases and check that its bank balance matches the total value of the remaining coins in circulation."
In Stellar, this service is provided by the ledger and the nodes that validate it.
There are other interesting features of the Stellar native currency such as providing a way to transparently convert between currencies when making a payment: https://www.stellar.org/how-it-works/stellar-basics/explaine...
You also need exchanges for cryptocurrency[1], so why not admit it from day one and build that concept into the system?
And maybe it's possible to graft a cryptocurrency onto SCP by using consensus to choose nodes which receive freshly "mined" currency.
[1] The mythical closed-loop Bitcoin economy ain't going to happen.
Everyone can run a node, but the whole system is not itself decentralised, because you need "anchors", which are banks or payment processors, to get your money in and out of the system.
So then, what is the point of the decentralised ledger? GNU Taler seems like a more simple solution.