Character.AI is a platform for open-ended conversation with AI characters. Users pick from a library of characters made by other people or build their own with Quick creation mode or Advanced creation tools, and interact through text chat and voice calls.

Character library - chat with characters for tutoring, stories, role-play, language practice, and brainstorming.
Creation tools - make a character in under a minute or fine-tune behavior with attributes, definitions, and personas.
Voice calls - talk with characters by voice in addition to text.
Mobile apps - chat on the web and on iOS and Android.

It is used by people who want interactive AI companions and creative role-play, and by creators publishing characters for others. The free tier covers chatting with the full character library; a c.ai+ subscription at $9.99 per month or $94.99 per year adds priority access, faster responses, better memory, and an ad-free experience.