Flex is a tool for creating dynamically realigning layers in different layouts.
Flex Line Rigs are all about working with single rows or columns, whereas Flex Grid Rigs are for more complicated scenarios in which you have multiple rows or columns operating as a cohesive system.
Flex is a collaboration between Vincent Raineri & Zack Lovatt
A Line Rig will connect all of your selected layers together into a straight line.
Then you can quickly & easily have the size of one layer affect the scale and position of its neighbours, creating a nice flexible line.
If a Line Rig is too 1-dimensional for you, try a Grid Rig!
Flex Grid Rigs will take your existing layouts and create horizontal and vertical controllers for them, letting you dynamically flex groups of layers as rows and columns.