Mathcad Integrates with Solidworks, Microstation, Ansys, Excel, Labview, and Stresscheck. I wish it would integrate with a 2D drawing program however....
Some people use references in Excel to link to other sheets within the document. Mathcad can reference entire worksheets with variables into a different worksheet. For a real dumbed down example: Place A=3 in a worksheet called ws1.xmcd Open up the second document and open the Insert menu->and...