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Comparison chart with key features:

Evaluation Worth Using?	Plugin	Math Formulas	Inline Editing	Works in Mobile	Filtering	Comment
To Test	CelesteCS Math					Looks promising...
No	Bob Swift Advanced Tables	Add only is not enough. Vote for multiplication.				Like the most but requires math functionality.
YesNo	Excellentable					Nice search function but ugly.
No	Spreadsheets for Confluence					n/a
To Test	Table Filter and Charts

So far all these are pretty limiting.

...

Yes this generally works but sharing spreadsheets for editing requires sharing in Google and has some limitations (forget now), but not for Corporate Websites.

Encryption

Looks promising, no public key, but simple enough - https://marketplace.atlassian.com/plugins/com.prcpo.confluence.plugins.secure-content-block

Form Capture

http://confluence.atlassian.com/display/CONFHOST/Capturing+data+with+forms - seems to have a good run down of the available options.

http://blogs.atlassian.com/2009/05/confluence_wufo/ - expensive but looks to be very powerful and mature. Video demo on home page. Requires an additional server.

Workflow

Still looking, have not tried anything yet.

Improved UI

Looks promising - https://marketplace.atlassian.com/plugins/com.brikit.themepress/server/reviews