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Tableau's biggest competitor is PowerBI, not anything open source.

OSS BI like Redash, Superset, Metabase, etc. Low code solutions like AppSmith.

Also retool, Budibase, glide and others

I don't think Retool and Glide are open source, but they are good alternatives to Tableau's pricing.

Excel (incumbent), and Looker (for anyone on Google)

Okay, but neither of those are open source...