The Prusa i3 is the third iteration of Josef Průša's RepRap 3D printer design. This is an open source design, the tag should be used regardless of individual manufacturer (clarify in the question if it is useful to be specific).
The design of the i3 focuses on ease of construction and use rather than maximising the number of self replicated components. As summarized in the RepRap wiki, the following is a list of the main improvements made upon the Prusa Mendel Iteration 2:
- Enhanced frame rigidity (prevents x-axis backlash)
- Easy assembly
- Parametric files for multiple sizes/bearings or bushings