Currently, I have to differentiate between IGoogle itself, Ning, Orkut & Hi5. They are the only containers that I can access as of now. If you know of more, please let me know!

To distinguish among them, I use the following strategy:

• following this sample, I parse as an associative array the arguments of the url (located at "window.location.search.substring(1)")  used to launch the gadget. Then, I get the value of the key 'synd'. It give either: 'ig' (for igoogle), 'hi5' or 'orkut' as of now. So, already 3 out of 4 identified!
• then, for those like Ning that don't run their opensocial APIs with the gmodules infrastructure, I obtain the url argument with key 'location' and look for known string (currently 'ning') to identify the last one.

That's the most "container-orthogonal" way that I found up to now, I you have any better way, let us know!

So, if you want to verify the compatibility of your latest widget with the opensocial API and Orkut, here is the procedure

• obtain a Google Accounts userid / password to log in in case you did not already get one through GMail, Analytics, Adsense, etc...
• go the homepage of Orkut, login and create your profile on the "productive" Orkut
• then, go to this page of the opensocial project to request access to the Orkut sandbox
• when you get the invitation from Orkut in your mailbox, you can now connect to the Orkut sandbox (located at sandbox.orkut.com)
• click the application button in the sidebar to access gadget configuration

• enter the URL of your gadget into the box left to the button 'Add Application'

• then, click on this button 'Add Application'

• your gadget now appears both in the list of configured applications and in the sidebar

• to run your test, you can now click on the new button named like your wadget (through the use of the title attribute in the xml configuring the gadget)

If you need a very simple gadget to start with, you can always access my "Hello World" gadget on the Download page of this blog.

Based on the page of Hi5's developer site, here is how to access their sandbox for testing the compatibility of your new opensocial widget with their container:

• get a regular account on Hi5 to create a valid pair of userid / password
• go to http://sandbox.hi5.com and log in with userid /password
• when logged in, click on 'MyProfile'

• click then on Tab 'Applications'

• now, you can test your widget by entering its URL in 'Add External'. Here is what I get for my "Hello World" widget

PS: the cat showing off on some screenshots is Unique, the family's Maine Coon