If you aren't sure which version you need, these are the most significant "milestone" releases in Blender's history:

While many software companies hide their legacy builds, Blender—being open-source—makes accessing its entire history remarkably easy. Here is everything you need to know about downloading and using old versions of Blender. Why Download an Older Version of Blender?

💡 For Windows users, download the .zip version instead of the installer. This allows you to run the old version as a "portable" app without overwriting your current Blender installation. Key Milestone Versions

You don't have to uninstall your current version of Blender to use an old one. Follow these steps to keep a "library" of versions:

Many powerful community-created addons are designed for specific Python versions. If an addon hasn't been updated for the latest release, you'll need the matching older version to use it.

The "Great Overhaul." This version introduced the modern UI, the Eevee real-time render engine, and the industry-standard left-click select.

The pinnacle of the "old" interface. It is the last version to include the Blender Internal Render Engine and the Blender Game Engine. It is famously stable for older computers.

Some users still prefer the pre-2.80 "right-click select" era or specific tools like the internal Blender Game Engine which was removed in newer releases. Where to Find the Blender Version Archive