Not GP, but I presume they're talking about alternative currencies¹. Things like the Ehki in Bilbao or Eusko across the border in Basque France. I'm picking those two on purpose because they make a point about it sometimes simply being about regional politics and not generic fiscal localism².
Depending on how you draw the line you could, for example, include the Barcelona Rec³ too. I think I draw the line at physical notes, but YMMV.
Edit to add: Looks like the ehki is digital only now.