Metabase is an Open Source business intelligence and analytics tool. It supports a variety of databases and services as sources for data, and provides a number of data querying and processing tools. Have a look at the GitHub repository as well.
And if you want a few alternatives or complimenting tools, I found this list quite useful.
A Comparative Analysis of Top 6 BI and Data Visualization Tools in 2018 looks at 6 most popular business intelligence and data visualization tools and compares pros, cons, features, pricing and more. The systems included in this review are:
Indexed has a very simple chart, explaining why everybody needs friends:
It’s not often that I need to draw a diagram or a flowchart these days. My time is mostly consumed by more technically challenging tasks. And whenever I do have to produce some form of a chart, I usually fallback on to the Graphviz dot, which allows me to do something in literally seconds.
However, I’m pretty sure the day will (or, rather, return) when I’d need a tool to produce eye-pleasing diagrams and flowcharts. For that day, and for that day only, I’m leaving the link to SmartDraw here. It’s a commercial offering, but at $15/month for their cloud-hosted web-based application, it’s seems to be quite a bargain.