There are several tools and platforms you can use to build knowledge-based AI systems, many of which offer free tiers or are open-source. Here are some notable options:
1. **Natural Language Processing (NLP) Libraries:**
- **spaCy:** An open-source NLP library in Python that provides pre-trained models for various languages and enables tasks like part-of-speech tagging, named entity recognition, and dependency parsing.
- **NLTK (Natural


