The Bolt-On plugins are a key part of SFXEngine, transforming the vanilla program into a hugely powerful sound-effect creation tool.
This week all 10 items of Bolt-On DLC are on sale, with an additional discount for the Bolt-On full set bundle too.
https://store.steampowered.com/bundle/38164/SFXEngine_Bolton_Full_Set/
Offer ends March 5th.