$EmbeddableServices
gives a list of external embeddable services that can be accessed through EmbeddedService.
Details

- The strings that appear in $EmbeddableServices define possible first arguments to EmbeddedService.
Examples
Wolfram Research (2015), $EmbeddableServices, Wolfram Language function, https://reference.wolfram.com/language/ref/$EmbeddableServices.html.
Text
Wolfram Research (2015), $EmbeddableServices, Wolfram Language function, https://reference.wolfram.com/language/ref/$EmbeddableServices.html.
CMS
Wolfram Language. 2015. "$EmbeddableServices." Wolfram Language & System Documentation Center. Wolfram Research. https://reference.wolfram.com/language/ref/$EmbeddableServices.html.
APA
Wolfram Language. (2015). $EmbeddableServices. Wolfram Language & System Documentation Center. Retrieved from https://reference.wolfram.com/language/ref/$EmbeddableServices.html