The ParaSail core is under the GPLv3,
but the ParaSail stdlib is in public domain. A citation of Tucker Taft
https://archive.is/qFoTG (the quote can be seen by clicking on the text of one of the visible comments and then by scrolling downwards with arrow keys)
Actually there is no GPL copyright notice on the ParaSail standard
library. I'll see what words need to be added to the copyright notice
to make it clearer that the ParaSail standard library can be freely re-used.