hadoop.apache.org
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Official Apache Hadoop project page for the open-source framework enabling distributed storage (HDFS) and processing (MapReduce/YARN) of big data. It offers documentation, downloads, getting-started guides, and ecosystem resources to help you deploy and use Hadoop.
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Databricks Community
Free Spark resources and notebooks
Apache Kafka
Official site with guides
Apache Spark Documentation
Official free docs and tutorials
Apache Spark with Scala
Learn Apache Spark with Scala! Master big data processing with hands-on examples from expert Frank Kane.
Big Data
Coursera course: Big Data Analytics
spark.apache.org
Apache Spark's official site is the home of the open-source unified analytics engine for large-scale data processing. It offers downloads, detailed documentation, tutorials, API references for Spark (SQL, PySpark, R, Scala), and guidance to get started or contribute.