I have a data frame with pivots that I'd like to visualize. What is a good openSource tool to use?
hortonworks data platform ships with zeppelin with a variety of interpreters. Spark Sql and data frames can be used to visualize the data using this notebook.
The question is difficult to answer objectively (what's the best?), however, there are a few options. The question caption includes PICOTS. PICOT s a technique medical researchers use to develop a clinical research question. I believe you did not mean that. The description of the question clarifies it as "pivots". In case that you really meant that you are using pivots for PICOT, let us know.
As Satish also suggested, Zeppelin notebook which also ships with Hortonworks Data Platform: http://zeppelin-project.org/
Others are: https://jupyter.org/
Both allow you to embed d3js widgets.
Even is not open source yet, the old Excel is also an option. Read this: http://www.simba.com/wp-content/uploads/2014/11/Simba-ODBC-Driver-for-Spark-Quick-Start-Guide-for-Wi...
Bottom line, if you already use Hortonworks Data Platform, Zeppelin makes the most sense.