DeepSeek

What it does

The chat front end for DeepSeek's models, notable because the weights are published openly and the model shows its reasoning trace as it works, which is unusually instructive when you are checking a maths or logic answer. It is strong on code for something that costs nothing. Sign-up needs an email or phone number, and conversations are processed on servers in China — worth knowing before pasting anything confidential.

Best for

• Maths and code questions
• Seeing a model's reasoning steps

Where it stops