Hi @rtbfreitas
Yes, Jeet, Neat, and Susy are all grid frameworks. Their role is to automate and simplify the building of website layouts, and they have some advantages compared to the grid systems used in Bootstrap, Foundation, etc.
A ready-to-use framework such as Bootstrap offers a ready-to-use grid. This means that you have to build your layout with predefined classes and default grid settings. You can change some settings but the amount of control is minimal. On the other hand a grid framework such as Jeet gives you complete design freedom in terms of more flexible syntax, custom grids, etc. In short, grid frameworks offer more flexibility and more control. Also they provide more advanced features such as asymmetric layouts. But this comes with a price. Such frameworks depend on preprocessors. In our case Stylus and Sass. So in order to use them you need to have the needed preprocessor installed and to know how to use it.
I hope this was helpful to you.