Our startup, rowzero.io, easily handles tens of millions of rows and is a subset of Excel. Leave us feedback in the app if there are any missing features you need.
A relational database. Excel data generally maps well to an RDBMS. You can run sqlite, MySQL, or PostgreSQL locally on a typical desktop/laptop.
Excel can serve as the front-end to a “real” database.
Use PowerQuery/PowerPivot/DAX.
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Well, there are the HPC Services for Excel, were you can offload calculations to an HPC Cluster and support more rows. https://learn.microsoft.com/en-us/powershell/high-performanc...
its not an alternative, but maybe it helps for your use case.