They're cousins, not clones. Each is built by a different company with different priorities:
ChatGPT (OpenAI) — the most widely known, with the strongest ecosystem of plugins and integrations. Very strong at general tasks and coding.
Claude (Anthropic) — known for thoughtful long-form writing, careful reasoning, and a strong safety posture. Often preferred for analysis, drafting, and nuanced work.
Gemini (Google) — deeply integrated with Google Workspace (Docs, Gmail, Sheets) and strong at multimodal tasks involving images and video.
Copilot (Microsoft) — embedded directly inside Microsoft 365: Word, Excel, Outlook, Teams. The default choice if your workflow lives in Microsoft tools.
Their core capabilities overlap by 80%+. The real differences show up in personality, integrations, and edge cases — not raw intelligence.