Nope, this is NOT an April Fool's Post.
If you go to the Frog God Games web store and use the code: ANNIVERSARY-40 at checkout, you get 40% off damn near everything in the store (I think there is ONE exception - Tome of Wonderous Items).
Still, looking to get the Swords & Wizardry Complete Boxed Set? 40% Off
Bard's Gate for S&W? Yep, 40% off. Rappan Athuk for S&W? 40% off.
Yep, all of the S&W titles in stock are 40% off. So are all of the 5e products (except as mentioned above.
The sale goes through the end of the month, so if you haven't yet decided how to spend your Tax Refund, the Frog God 40% off Sale might be a good option ;)