Zendesk's startup program gives early-stage companies free use of the Zendesk Resolution Platform for up to 50 agents. The baseline term is 6 months. Startups affiliated with a VC or accelerator partner can get 1 or 2 years, depending on the partnership, team size and funding stage, by applying through that partner's referral link.
No credit card is required upfront. When the term ends you need to choose a paid plan to keep your account. Zendesk may revoke the offer if your company does not meet the requirements.