DOC: ecosystem.rst: Koalas

Author: HyukjinKwon

doc/source/ecosystem.rst

@@ -313,6 +313,15 @@ Increasingly, packages are being built on top of pandas to address specific need
  * vaex.from_pandas
  * vaex.to_pandas_df
 
+`Koalas <https://koalas.readthedocs.io/en/latest/>`__
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+The Koalas project implements the pandas DataFrame API on top of Apache Spark so that data scientists can be more productive when interacting with big data.
+pandas is the de facto standard (single-node) DataFrame implementation in Python, while Spark is the de facto standard for big data processing.
+With this package, you can:
+
+ * Be immediately productive with Spark, with no learning curve, if you are already familiar with pandas.
+ * Have a single codebase that works both with pandas (tests, smaller datasets) and with Spark (distributed datasets).
 
 .. _ecosystem.data_validation: