Zendesk
(User)
Zendesk is a very popular customer support service (helpdesk).
MailChimp
(List Subscriber)
MailChimp is a very popular Newsletter mailing service.
Use FoxWeave to easily Sync Users in Zendesk to List Subscribers in MailChimp

Cloudant DB

FreshBooks

Google Forms

Google Mail

HTTP

MailChimp

MongoHQ DB

MySQL DB

Oracle DB

OnePageCRM

PostgresSQL DB

Salesforce.com

Sendgrid

MS SQL Server DB

Webhooks

Wufoo

Twilio

Twitter

Zendesk