Following the Grid RowActions plugin I turned out first version of CellActions.

To clarify:

RowActions should be used when we need to operate on a whole grid record.
CellActions should be used when we need to operate on a single grid cell.

You can use one, another or both of them in one grid.

Demo: http://cellactions.extjs.eu

Note: Code is really beta in this case, not fully documented and not for general production use. I'll give it some lifetime here and then I'll polish it.
Code is fully documented and well commented now.

Enjoy!