ChatGPT
OpenAI's chatbot, released November 30, 2022. Built on GPT models (3.5, then 4, 4o, 4.1, 5). Triggered the modern LLM era.
Fastest product ever to 100M users (Jan 2023). Free tier + ChatGPT Plus ($20/month) + Teams + Enterprise. Multimodal since 4o (2024): voice, images, video. Custom GPTs (2023), GPT Store (2024). Competitors: Claude (Anthropic), Gemini (Google), Copilot (Microsoft, built on OpenAI), Perplexity, DeepSeek. OpenAI's drama with Sam Altman's firing November 2023 → back within 5 days.