I've fully rewritten the spreadsheet tool, available at usecarlo.com:

The major improvements are:

• More flexible input format
• Interactive — histograms update as you edit the spreadsheet (this also means you can collaborate in real time)
• Overhauled UI with dozens of new features

Other improvements include:

• Simulations run many times faster — this is especially noticeable for the sensitivity analysis
• You no longer need to manually type in the result cell coordinate
• Multiple output variables are now supported