KNIME.
https://www.knime.com/
Knime is a nice ETL + reporting tool, all in one, that's free and seems to be the most easy to use.

Talend.
https://www.talend.com/products/talend-open-studio/
Talend is an ETL tool, well known and with serious maturity.

Knowage.
https://www.knowage-suite.com/site/licensing/community-edition/
A nice tool with community edition Knowage CE. Try it to see how a real BI tool looks like. (needs JAVA_HOME to point specifically to java 1.8 however)


Pentaho Suite. A suite of tools: Mondrian as an OLAP server, Kettle for ETL, Reporting for reports.
https://community.hitachivantara.com/s/article/data-integration-kettle
https://community.hitachivantara.com/s/article/pentaho-reporting
https://community.hitachivantara.com/s/article/mondrian
IMHO Mondrian is fairly hard to setup and use -- however it served as the basis for several FoSS tools during the late 00's and 10's. Frequently reported to have been used with Saiku Community Edition, a reporting front-end.

Instead of mondrian, it's possible to go for Xmondrian. The Foodmart db is already included in it. You need to have installed Apache Tomcat and, inside its webapps folder, create a folder xmondrian, copy and unzip the xmondrian.war inside it.

SAIKU: https://community.meteorite.bi/
XMONDRIAN: https://github.com/rpbouman/xmondrian


MISC: https://logz.io/blog/business-intelligence-tools/