In relation with page http://tayeb.fr/informatique/collaboratif.htm
I began to write this document in January 2007. I update it from time to time, but there is certainly some outdated information.
If you want to contribute, please make a copy of this spreadsheet, make your modifications, highlight the cells you have changed (see next line), and mail it back to me (my email is given in the links at the top of http://tayeb.fr). I will put it online quickly. 
Example of highlighted cell (see previous line)
This greyed lines are out of purpose:
You are invited to complete this document with the information coming from your experience. For this purpose, you can:
- best solution: make your own account on http://sheet.zoho.com, then send me (http://tayeb.fr/coordonnees.htm) the email address of this account in order that I share the document with you,
- you can write me (http://tayeb.fr/coordonnees.htm) and I will send you an invitation to share this document,
- last, the not recommended way: connect on http://sheet.zoho.com with the ID internetshared and password websharedb
Zone de Texte: All these "online" applications lack for a feature that is essential for me: I want to index all the documents that I work on (in order to find all this information scattered in different places). To this way, I use a "desktop search engine" that indexes all my local files. It would be useful to have an option in order to automate a periodical download from the web version to the local hard drive.
Spreadsheets applications (Excel like) for collaborative work        
Functions Zoho Sheet Thinkfree Google Documents
Google Apps[1]		 EditGrid
Presentation http://www.zoho.com http://product.thinkfree.com/online/overview.html http://docs.google.com/support/spreadsheets/ http://www.editgrid.com
         
Comments in the cells Y  Y  Y / N [2] Y 
Automatic filter N  Y  N  Y [3]
Online edition Excel like (extremely simplified) Excel like Basic  
Deported edition Excel[4]   N  Excel[5]
Compatible with Excel macros N  N  N  N 
         
Text        
"Insert text box" N    N  N 
By default, text continues on adjacent cells if they are empty N [6]   Y  Y 
Rotation[7]   N    N 
         
Simultaneous edits[8] Y  Locked[9] Y [10] Y [11]
Chat interface Y      Y 
RSS[12] N [13] N  Y [14] Y / N [15]
Email notification[16] Y  [17] N  Y [18] N 
Versions[19] Y  Y  Y  Y [20]
Differences between versions[21]   N  Y / N [22] N 
Non registered users can edit?       Y [23]
Password protect sheet for edition?     N  Y [24]
         
Import     xls, ods, csv  
Export     xls, ods, csv, pdf, html  
         
Good For MS Office editing on your own computer, with only 1 person editing. Functions very close to Excel's ones. Can send you RSS notifications when the file is modified.  
Bad Some problems with the comments editing.[25] Poor documentation.
Not usable on the connexion by my university: uses some protocol recognized as a Peer to Peer protocol, that is filtered => work cannot be saved.		 Date in US format. You can get it in French format, but you must accept a comma as decimal separator (I want a dot!). Solved (does not seem to occur anymore on dec. 2007): if you copy a cell, then paste it in another cell, accented letters were often replaced by ? (question marks)
Bad Comment import problem with "[26]      
Bad Problems with some text (hyperlinks) that do not appear with IE (still in 01/2009).      
Bad Problems with some actions not recognized with Firefox and IE  (still in 01/2009).[27]      
Text editing (Word like) applications for collaborative work        
Functions Zoho Writer Thinkfree Google Docs Office Live
Presentation http://www.zoho.com http://product.thinkfree.com/online/overview.html http://docs.google.com/support/spreadsheets/ http://www.officelive.com
         
Comments in the cells        
Online edition Word like (extremely simplified)[28] Word like    
Deported edition Word[29]     Word
         
Simultaneous edits[30] Y    Y  Locked[31]
Chat interface Y       
RSS   N  Y   
Email notification   N     
Versions[32]     Y   
Differences between versions     Y, different colors for each editor  
         
Import > 4 MB[33]   500kB max size for imported .doc[34]  
Export        
         
Good For MS Office editing on your own computer      
Bad Don't work with Firefox[35]      
Wiki      
Functions Zoho Wiki    
Presentation http://www.zoho.com    
RSS Y     
Email notification Y [36]    
Differences between versions Y     
Simultaneous edits N [37]    
Attachments Y [38]    
Notes Can embed Word and Excel files.
These Word and Excel files can be edited directly from the Word and Excel applications on the user's PC.		    
Notes Can be used to share html pages (use button "Insert html"). Example: http://gt13013.wiki.zoho.com/Chargeur-accus-RS900.html    
Bad Problems with Firefox[39]    
Zone de Texte: As soon as there will exist an online spreadsheet application with all the features above in green, this file will go on this application and will be editable online by everybody !
[1]
gt: Google Apps offers the same features as Google Documents, plus some more...
[2]
gt: You can put comments, but they are lost when importing the file from Excel to SpreadSheeets.
[3]
tayeb: new feature since Nov. 2008. To use it, it seems that you must first select the cells where you want to apply the filter.
[4]
tayeb: you can edit the online documents on your own Excel application with the plugin: great !
But you loose the simultaneous editing possibility...

[5]
tayeb: I have not yet tested this feature. See
http://www.editgrid.com/site/news/excel_plus_launch

[6]
tayeb:
One needs to "Merge cells across", but then it is imposssible to add a column.

[7]
gt:
useful in order to build spreadsheets like this one:
http://tayeb.fr/informatique/partage_fichiers.xls
[8]
"Y" means that several authors can edit the document simultaneously.
[9]
tayeb: the sheet is locked by the first person who opens it. The other authors can open it only in read only mode.
[10]
tayeb:
50 persons can edit simultaneously.
Last save wins (per cell).
[11]
gt: Last save wins (per cell).
[12]
gt: get RSS notification when the file is changed
[13]
gt: april 7th, 2007: RSS feeds are implemented only for feeding the sheet with external data.
[14]
gt: via the Publication menu. But I haven't be able to make it work.
[15]
gt: it seems that one can only follow his own spreadsheets: http://forum.editgrid.com/viewtopic.php?id=572
Moreover, it is not documented. But I use it and it works. Syntax: http://www.editgrid.com/feed/spreadsheets/user/gt13013
[16]
gt: get an email when the file is changed
[17]
gt, 21/05/07: Zoho announcement:
"We have also enhanced our collaboration module allowing you to personalize the email message being sent while sharing a spreadsheet. You can configure it to fire email notifications when someone modifies your shared spreadsheet. "
[18]
gt: with plenty of options (feature added on March 19, 2008) :
http://groups.google.com/group/GDSupdates/browse_thread/thread/a7d84adf5cbc9674/bd00ace1c68b08cf?lnk=gst&q=

Quite interesting: when somebody changes the sheet, you can get an email, with a link pointing to the sheet, where the changed cells are highlighted. Great!
[19]
gt: stores and can go back to any previous version of the document
[20]
gt: Property view > History
[21]
tayeb: I'd like to have the ability to:
1. select two versions in the history,
2. get the differences between the two versions,
3. with highlighted text whose color tells who made the changes.
These features are available in Google Docs (for text documents), and it is fantastic!
Even without point 3 above, it would be great !

[22]
gt: Only between two successive versions, but you cannot get differences between 2 arbitrary versions.
[23]
gt: plenty of options available
[24]
gt: allows to share to an email mailing list, by sending an email containing the password.
[25]
tayeb: I am in contact with Zoho support for this problem since 1-march-07, but it is still not solved (on 12-oct-07).
I have also opened a thread in the forum:
http://forums.zoho.com/viewtopic.php?t=70142
[26]
tayeb, april 7th, 2007: import from Excel of commented cells where comment contains the " character leads to truncation of the comment after the first " character.
[27]
gt: example: Edit a spreadsheet > Partager > Modifier les détails partagés > The changes on the option "Notify me, whenever a shared member modifies this spreadsheet" are mostky not saved.
[28]
tayeb: for instance, in the 1.2 version, there is no "Format" menu
[29]
tayeb: you can edit the online documents on your own Word application using the plugin: great !

[30]
"Y" means that several authors can edit the document simultaneously.
[31]
When one of the co-authors edits the document, the document is locked for the auther authors (and they are advised that somebody else is editing).
[32]
gt: stores and can go back to any previous version of the document
[33]
gt: I have imported .doc files of 4MB without any problem
[34]
Tayeb: if you import .doc files, they must not be bigger than 500kB
[35]
tayeb: I am in contact with Zoho support for this problem since 1/03/07, but it is still not solved (on 25/03/07).
Works fine with Internet Explorer.
[36]
gt: the administrator is  notified by email once a day of the changes done to his/her wiki pages (feature added on July 16th, 2007). This is the default behavior, but the notification can be disabled.

gt (01/2008): The Wiki Administrator/Owner can now choose to receive mails once a page gets edited or commented upon. Feedback mails can now easily be sent to the Wiki owner. To control spam, the feedback mail form is captcha protected.

[37]
gt: January 2007: the rule was: last to save wins.
August 2007: still the same. I wrote a comment on http://wiki.zoho.com/WikiFAQ.html
and I opened a bug-report discussion on
http://forums.zoho.com/viewtopic.php?t=123029
http://forums.zoho.com/viewtopic.php?p=179094

Should be tried again later in order to see if it has been improved.
[38]
http://wiki.zoho.com/Attachments.html
[39]
tayeb: I am in contact with Zoho support for this problem since 1/03/07, but it is still not solved (on 25/03/07).
Works fine with Internet Explorer.
It seems that the problem occurs only with Firefox and when a Zoho Sheet is embedded in the Zoho Wiki page.