Now you can add anyone to new or existing wave even if he is not in your contacts. An invitation will be sent to him to join Google Wave with the description of wave.
The APIs stuff is just making life easier.
Gadgets are like small applications we play with at different platforms.
Google already have gadgets platform available at iGoogle. Now google introduced Gadget Ads for Adwords. Now you can have more interactive ad campaigns with gadget ads.
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Ad ADT Adword AJAX Android API balancing Binding Calling Class Column Configure Copy Curl Data Database Eclipse Error Gadget Google Hello ini ini_set Install Invite Javascript Late Linux Load Master Method MySQL Output PHP Playground Proxy Replication SeaMonkey Server Slave Static String Table Ubuntu upload_max_filesize