Another top contender is TLDR, an IDE plugin that uses AI to explain code elements that might be hard to understand in plain English. It works with nearly all programming languages, and it's particularly good at explaining regular expressions and SQL queries. TLDR offers a free version with limited API credits and several paid plans so it's available to solo programmers and bigger teams.
If you want multi-language support and a broader collection of AI-powered coding tools, ZZZ Code AI is worth a look. It supports a broad range of languages and offers tools like AI Code Explainer, AI Code Debug and AI Code Documentation. It's available online for free, though it has usage limits to prevent abuse.