ChatGPT (OpenAI)

The tool that started the AI revolution. ChatGPT hit 100 million users in two months (the fastest consumer app adoption in history) and now has 200+ million weekly active users. GPT-4o and GPT-4.5 handle everything from writing emails to analyzing spreadsheets to coding entire applications. The $20/month Plus subscription is the most impactful $20 most knowledge workers spend. Enterprise adoption crossed 92% of Fortune 500 companies by 2025. The biggest time saver: "draft this for me" — first drafts of emails, reports, summaries, and code in seconds. Not perfect, but 80% there in 5% of the time.