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Drawing - Gliffy
Prototyping - Balsamiq
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Evaluating
Spreadsheet Functionality in Tables
Comparison chart with key features:
| Using | Plugin | Math Formulas | Inline Editing | Works in Mobile | Auto-numbering | Comment |
|---|---|---|---|---|---|---|
| Yes | Bob Swift Advanced Tables |
|  | | | Like the most but requires math functionality. |
| Yes | Excellentable | | |  | (as far as I can tell) | Nice search function but ugly. |
| No | Spreadsheets for Confluence | | | | | n/a |
So far all these are pretty limiting.
How about embedding google spreadsheet into the page and see if it can be edited live?
Encryption
Looks promising, no public key, but simple enough - https://marketplace.atlassian.com/plugins/com.prcpo.confluence.plugins.secure-content-block
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