Zendesk
The enterprise suite
Omnichannel by design — email, chat, voice and social — with a huge app marketplace and deep configurability. Priced per agent across Suite tiers (~$55–115/agent/mo on annual billing), with AI as a paid add-on, and enough admin surface that larger deployments often involve a consultant.
Best for: teams that need phone and social channels in the same tool, or depend on marketplace apps.