This version represented the final refinement of the generation before the transition to Stacks 5 . It is often cited as a highly stable "long-term" version for users on older macOS versions (like Catalina) who needed a reliable environment before moving to the newer API of Stacks 5.

: Create flowing columns, flexible rows, and image grids.

: Patched several crashing bugs related to the Undo command and errors that occurred just before RapidWeaver shut down.

: Supports thousands of third-party stacks (e.g., sliders, menus, forms) from various developers. Key Improvements in Version 4.2.5

: Fixed an issue where form elements with autofocus would "steal" the insertion point during editing sessions.

Stacks allows users to build responsive, complex web pages by nesting "stacks" (individual content blocks) within one another.