I'm just going to go ahead and say it - nothing comes close to Microsoft Excel in terms of the impact it has had on the world.
When I entered the work world, I was shocked by how many careers and industries relied on it. I used to think it was just used by accountants and finance people. Nope. Marketers, project managers, chemists, sneakerheads, brides, academics, technicians, store owners, and even VFX artists use it daily to track and manage information.
I think part of the reason people use it so much is because it's so versatile. Even though it takes some learning initially to get started, it's still surprisingly simple and powerful. Really, I've always seen Excel as some cross between a calculator as well as a “layman's mini database". It allows ordinary people to query data which might not be big enough to justify its own database (most ordinary people don’t even know what a database is, if I’m being honest). It's a great planning tool. Also, people use it to draft and lay out any kind of decision which might have numbers involved.
I'm also convinced Excel is one of the big drivers of corporate “buy-in" for Office 365 and Windows itself, keeping the entire Microsoft ecosystem afloat, but that's another post, for another day.
Why is it so underrated? I think this is because the tool itself doesn't really reflect the diversity of its audience and use cases - it still acts like a mostly boring finance tool. Also, most people just don't see it as one of those universal consumer-like tools such as Paint or Word because working with numbers is, honestly, just not as exciting. But it is, it really is one of the great, universal software programs everyone has used at some point in their life.
Sure, a lot has changed in the world with new competition like Airtable, Google spreadsheet, and even Notion, but I still think Excel is here to stay. Simple, versatile advances like Excel just have a way of sticking around.