(Updated) Use Google Docs to host and edit your KML files. Gmap4 immediately displays your updated map.

[Joseph Elfelt]

You can now (1) place your KML files online as Google Documents, (2)
use the editor within Google Docs to change your KML file, and (3)
immediately see your revised KML data with an enhanced Google map
viewer. The Gmap4 viewer is free and has no ads. Since it runs
entirely online there is nothing to buy, nothing to download, nothing
to install. Detailed topographic maps are included for the USA and
Canada (courtesy of the MyTopo Company).

Since Google Docs gives the owner of a file the ability to grant
editing permission to others, working in this environment would be one
way for multiple people to add information to the same KML file.

Homepage: http://www.mappingsupport.com/p/gmap4.html
PDF ‘Help’ file: http://www.mappingsupport.com/p/gmap4_help.pdf

The step-by-step instructions for uploading a KML file to Google Docs
begins at the bottom of p.12 of the ‘Help’ file.

Here’s the 30,000 ft workflow:
1. Open a browser tab and upload a KML file to Google Docs following
the instructions in the Gmap4 ‘Help’ file.
2. Open a second browser tab and display your KML file with this URL:
http://www.mappingsupport.com/p/gmap4.php?q=google,paste_Google_doc_id_code_here
3. Use the editor in Google Docs to change your file
4. Save the changes
5. See your changed KML file with this URL:
http://www.mappingsupport.com/p/gmap4.php?q=google,paste_Google_doc_id_code_here&refresh=1

Enjoy!