Vonage

Voice, messaging and video APIs alongside unified communications, from a carrier-scale business.

Communications APIs with a telecom behind them.

What it is sold for

Adding voice or messaging to a product.

The rest of payments and messaging, alphabetically. Sharing a category is a filing decision, not a relationship.

Ably

Hosted realtime messaging with delivery guarantees and presence, sold on what happens when connections drop.
Anymail finder

Finds work email addresses from a name and a domain, and charges only for the ones it can verify.
Applozic did not answer

Chat and messaging SDKs. The site presents an expired or misconfigured certificate and would not load.
Braintree

PayPal's payment platform for merchants who need cards, wallets and PayPal behind one integration.
EasyPost

One API across many carriers for rates, labels and tracking.
FormSpree

A form backend for static sites, so an HTML form can submit without any server behind it.
Heybounce

Email validation before sending, protecting sender reputation from hard bounces.
Hunter.io

Finds and verifies professional email addresses from a domain, one of the older tools in this category.

ImranTools[Vonage]