Top 6 C# Openxml Projects

NPOI

16 5,510 9.1 C#

a .NET library that can read/write Office formats without Microsoft Office installed. No COM+, no interop.
ClosedXML

26 4,407 9.5 C#

ClosedXML is a .NET library for reading, manipulating and writing Excel 2007+ (.xlsx, .xlsm) files. It aims to provide an intuitive and user-friendly interface to dealing with the underlying OpenXML API.

Project mention: When XML in Word Became Illegal | news.ycombinator.com | 2023-10-12

It's also country specific.
I work on Excel library and the text to number/date feature was one of less fun things to implement at least semi-correctly.
I remember my comment on the PR back then:
https://github.com/ClosedXML/ClosedXML/pull/1899

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MiniExcel

1 2,387 7.3 C#

Fast, Low-Memory, Easy Excel .NET helper to import/export/template spreadsheet (support Linux, Mac)
OfficeIMO

8 245 9.5 C#

Fast and easy to use cross-platform .NET library that creates or modifies Microsoft Word (DocX) and later also Excel (XLSX) files without installing any software. Library is based on Open XML SDK

Project mention: Get pagesetup header from a word document | /r/PowerShell | 2023-06-20

While I have method that allows easy find/search for stuff in headers - https://github.com/EvotecIT/OfficeIMO/blob/master/OfficeIMO.Examples/Word/FindAndReplace/FindAndReplace01.cs

ShapeCrawler

1 244 9.4 C#

🍂 A .NET library for manipulating PowerPoint presentations
BookFx

0 105 0.0 C#

Composing Excel spreadsheets based on a tree of nested components like the HTML DOM.

NOTE: The open source projects on this list are ordered by number of github stars. The number of mentions indicates repo mentiontions in the last 12 Months or since we started tracking (Dec 2020).