For an app to be added to Zapier, it must have an API that is REST or XML-RPC-based.
1. Zapier Support
You can reach out to Zapier Support to request a new app. While most apps on Zapier are built and maintained by the app developers themselves, Zapier keeps an internal list of app requests.
2. Zapier Trusted App Developers
If user demand is strong enough, but the app in question doesn't have the engineering time or resources to devote to connecting their app to Zapier, they can contract a Zapier Trusted App Developer to build a Zapier integration for them. Apps built by Zapier Trusted App Developers are on equal footing with every other app when they are globally activated.
3. Zapier Developer Platform
The Zapier Developer Platform is free for anyone to use to connect an app to Zapier, and is self-serve from creation to deployment. For simple apps with easy APIs, no code may be required.
While apps connected to Zapier without the official support of the app developer can't be made public in Zapier's App Directory, they can be used internally by you and your teammates.
If an app is not yet supported, there are several workarounds that may allow you to accomplish your goals:
Use a RSS by Zapier trigger to get feed information to and from the app.
Create a Zap with a supported email trigger (e.g., Gmail, Office 365, IMAP) and a filter that identifies emails sent from the app.
Use Email Parser by Zapier to parse information from these emails and add them as separate fields to your Zap.
If your app accepts new information by sending an email to an address they specify, you can use Email by Zapier to send new information to the app in an outgoing email.
Use 3rd party apps that post information to the app. For example, Buffer and Hootsuite will post information to other apps like Facebook and Instagram.