This is mostly out of date -- Zapier has lots of ways to do this without custom connectors:
* Formatter -- https://zapier.com/help/formatter/
* Filters -- https://zapier.com/help/filter/
* Webhooks -- https://zapier.com/help/webhooks/
* Code (JS/Py) -- https://zapier.com/help/code/ or https://zapier.com/help/code-python/
Plus if you want -- those custom developed apps can be added by anyone, for free: https://zapier.com/developer/.