What free AI tool actually impressed you?

Hi everyone...i have tried plenty of free software over the years.

Some were disappointing while others ended up being surprisingly useful. That's how i ended up keeping wps office installed instead of constantly searching for another microsoft office download solution.

Now I'm wondering about AI tools...what's a free and open-source AI project that genuinely impressed you after using it?

Not the most hyped project, but one you actually found useful. I'd love to hear your suggestions..