Adding text to models?

Different from Qubism I'd guess? It is free?

YOu can do extrude text in Sketchup, however, you would need to have your model in Sketchup native format.  You can't simply import a STL into a program and modify it easily.

You can however try these 2 approaches: 

1.  Raised Text
In sketchUp, do they text you want and extrude it.  When done, export it to STL.  Import the STL model you want to add the text to in Repetier, then import the text STL  as well. 

Using the Rotate, Translate and scale function under the Object Placement tab, align your parts as needed, then you can save the mix as a single STL object.

2.  Carved out text
Create your text in Sketchup as before.  Load the STL into netfabb, then click repair.  Using the shell selector tool, select all the parts, then click the "flip selected triangles" button.  This will effectively create a negative volume object.

Follow the instructions above to align the text and the object in Repetier, but this time make sure the text object intersects the body of your object.

When you slice this, the text, which has negative volume, will create a hole in your main object.

I'll try to post a quick example later.

123Design also

As n2ri said, you may want to try 123D Design. 

It has a text tool as well as being able to import .stl files.  I tested it on a simple flat surface of a .stl file and I could add raised & recessed text by using merge & subtract, respectfully.  You can even fill in recessed text if it's a flat surface, by merging a solid with the top surface flush to the .stl model.