The Saved Tools list of the Sequence Editor's left-hand side Tools Panel is a list of effect tools that you have saved for future use. Once on the Saved Tools list, a tool will remain there, even when you use the Sequence Editor again in the future, unless and until you remove it from the list.
Clicking on a tool listed in the Saved Tools list makes that tool active.
The Saved Tools list, with four saved color fades and five other saved tools
To put a tool on the Saved Tools list, right-click on its entry in the Recent Tools list, and select "Save Tool" from the popup menu that will open.
To remove a tool from the Saved Tools list, right-click on its entry in the Saved Tools list, and select "Remove Tool" from the popup menu that will open.