ProxyKingdom
Rotating Proxy API that produces a working proxy on every request

Push notifications for Android & iOS.
Pusher Beams API is a free Development API that requires apiKey authentication, is served over HTTPS and has unconfirmed CORS support.
A push notifications API for developers who need critical information delivered every time. Scalable delivery for all your apps with no complex integration.
Details from pusher.com.

Unified API suite · now live
Geocode an address, validate an email, track a flight or pull stock data with one account, one dashboard and one API key.
Rotating Proxy API that produces a working proxy on every request
QR codes and barcodes (Code 128, EAN-13, Data Matrix, PDF417 + more). SVG or PNG output
Free auto-updating list of live-tested proxies (HTTP/HTTPS/SOCKS4/SOCKS5), refreshed every 6 h
The Pusher Beams API is provided by Pusher Beams (pusher.com). A push notifications API for developers who need critical information delivered every time. Scalable delivery for all your apps with no complex integration.
Yes. The Pusher Beams API is listed in the Development category of the public-apis directory, which only includes APIs that are free or have a free tier. Check its documentation for rate limits and paid plans.
Yes. The Pusher Beams API uses apiKey authentication, so you need to register for credentials before making requests.
CORS support for the Pusher Beams API is unknown. Test a request from the browser, and fall back to a server-side call if it is blocked.
Yes. The Pusher Beams API is served over HTTPS, so it's safe to use in production.