I've been using Simplify3D for slicing STL files for several years now. I've really liked the software and have always felt it was well worth the money as I have lost far fewer prints using it.
I reinstalled my laptop with Ubuntu recently and so I was happy to see that Simplify3d has a Linux version as well.
Their install instructions were pretty minimal as they have a really nice installer that did most everything. After install though, I did not see Simplify3D show up in the list of applications.
Here are the steps I followed to manually add it:
1. Searched, found and downloaded a jpg version of their product icon and converted it to a png. I'll save you that trouble and you can right click and download this one instead:
2. Copy the downloaded image file to /opt/Simplify3D-4.1.2
$sudo cp ~/Downloads/simplify3d-icon.png /opt/Simplify3D-4.1.2
3. Create a .desktop file
$sudo vi /opt/Simplify3D-4.1.2/Simplify3D.desktop
and paste in this:
Comment=3D Printing Slicer
4. Now add the .desktop file to the Unity Launcher
$ sudo desktop-file-install /opt/Simplify3D-4.1.2/Simplify3D.desktop
That's it, now it will show up in the launcher!