The Mozilla Channel Messaging API allows two separate scripts running in different browser contexts to communicate directly as long as they're attached to the same document (e.g. two IFrames, two workers, or two documents via a SharedWorker). These scripts are able to pass messages back and forth across two-way channels with a port at each end.
The following is a list of SDKs from our SDK directory that matched your search term. Though your definition of an SDK may differ, in our world, we define SDKs as platform- specific tools for consuming existing APIs of the sort we list in our API directory. For example, the Ruby SDK for consuming the Twitter Ads API. If you think an SDK, API, or other asset is missing from our directory, be sure to check our guidelines for making contributions to ProgrammableWeb.