From the sales sheet:
Through the month of July customers can buy Peter Schweighofer’s system-neutral Heroes of Rura-Tonga pulp setting sourcebook at a 25% discount…just use the coupon good at the Griffon Publishing Studio e-storefront at DriveThruRPG.com
The coupon coincides with the release of a free/pay-what-you-want PDF Heroes of Rura-Tonga adventure, The Paranoia Pit, perfectly suited for almost any pulp setting or adapted to other genres.