Spring shortcuts are "press and hold" shortcuts that toggle a state when they are pressed and restore that state when the key is released.
For example, while using any tool, press and hold "S" to temporarily switch to the Selection Tool, change the current selection, the release "S" to continue working with a new selection.
Curver is still in development, but you can get immediate access and get involved right now! Provide feebdack and join discussions to help us evolve Curver into something truly unique and solid.
You can download the free public beta or purchase the Early Access release.