Honestly I don’t need to know anything about it at all except that it’s a payment system designed by GNU
Then you seem to know even less then you thought? GNU supports development, but each project is independently designed and developed. Taler’s roots are in academia.
Because it’s not a crypto-currency it is a lot more efficient: e.g. no need for wasteful proof-of-work or staking. So it certainly does not have all the downsides of crypto.
From what I gather, the licence is still in the spirit of open source
It’s not though. It’s wildly against it. The spirit of open source is that anyone can take open source code and use and modify it. This isn’t the case here.
Yet another alternative is jsonata.org