I used to work with Excel heavily, even with interactive, app-like documents, in the past.
All that was very nice and efficient, but I still would say that I only touched 10% of Excels capabilities.
Nowadays I still work with older Excel 2003, since this is the last mainly compatiblle Excel version,
for all the features I loved to use.
I try to move to LibreOffice instead, but only as spreadsheet and not with all VBA features, and
all my interactive features are broken nowadays.
Unfortunately either Excel, Office365 and LibreOffice were not able to give that light ease of use of the old Excel versions.
And I'm talking about the ease of use for inserting lines, formats, printing formatting, etc.
All that is gone now, or very much limited, where I see the old Excel still as perfect UI, which I even used
as replacement for Word in some cases.
I considered many times, to put my stuff into an Excel-replacement-app, but I think from the 10% I ever used, cut another 10%,
so even that remaining 1% of the normal Excel would be a too tough project.
Even is you use libraries from TMS or others, this is quite tough to re-implement the basic convenience features,
and still a lot of manual coding is needed.
I'm looking more towards solutions in HTML5, CSS, JavaScript right now, to make nice, interactive, print-friendly data presenstations,
where HTML seems to be much more flexible than Delphi could every be.
Always when I have to fill a PDF form, I think OMG, why on earth has Microsoft give away control over the spreadsheet market,
which they once 100% ruled, so that this ugly peace of modern PDF could happen.