3D Models
Pinshape : https://pinshape.com/
Cults3D: https://cults3d.com/
Thingiverse : http://www.thingiverse.com/
GrabCAD: https://grabcad.com/
Hardware
Reprap Org : http://reprap.org/wiki/RepRap
Reprap Printer “Prusa Mendel” : http://reprap.org/wiki/Prusa
Reprap Printer “MendelMax” : http://reprap.org/wiki/MendelMax
Extruder : http://www.thingiverse.com/thing:8252
Electronics
Sanguinololu Board : http://reprap.org/wiki/Sanguinololu
RAMBo Board: http://reprap.org/wiki/Rambo
Arduino : https://www.arduino.cc/en/Main/Software
Software (3D Printer)
Cura (3D printer control): https://ultimaker.com/en/products/cura-software
Repetier (3D printer control): http://www.repetier.com/
Slic3r (slicing engine): http://slic3r.org/
Firmware: https://github.com/ErikZalm/Marlin/ (please use only the included firmware as it is tuned for our machines)
Software (3D Modeling)
FreeCAD : http://www.freecadweb.org/
SketchUp : http://www.sketchup.com/
OpenSCAD : http://www.openscad.org
MeshLab : http://meshlab.sourceforge.net (STL mesh editing, cleaning, healing, etc)
NetFabb Basic : http://www.netfabb.com/downloadcenter.php?basic=1 (STL mesh viewer and auto repair. Check out their mobile app as well!)
Onshape : https://www.onshape.com/