This came up because I was sending a colleague a Word file from my Windows computer at work, and for some reason, it sent it as an .odt file, when in the past it has only ever sent .docx files. He couldn't open it on his iPhone. I had coincidentally just had the same problem receiving an .odt file on my iPhone from someone and trying to read it, unsuccessfully. I was able to open it on my MacBook at home, which defaulted to TextEdit, for which there is no iOS equivalent. iOS Mail has built-in support for .doc and .docx files, so it seems weird that Microsoft Office would be converting stuff to .odt. You'd think Apple would be more interested in it than Microsoft, considering Microsoft's Word is pretty much the standard. After researching it and reading the replies (Thanks!) it seems like no-one uses it much, despite efforts to establish it as a standard. I think it's a grand idea to standardize office document formats, something like when PDF went from "Please Download Adobe Reader" and ZIP files required Stuffit Expander. Now PDFs work everywhere, "seamlessly" and .zip archives are a similar non-issue. Why Apple continues to make Pages and Numbers is beyond me. RIP QuarkXpress, Adobe PageMaker, and hopefully soon Pages and Numbers. At work we have documents in both InDesign and Publisher, for some stupid reason. C'mon, people.
Here's my dream: PDF becomes a cross-platform, Windows, Android, Mac OS, iOS, Ubuntu, and every other OS standard text format that includes exact print formatting. All text-editing and typography/layout software automatically spits out pdfs, and all software is free. Every document you ever get, including emails, print exactly the way they are supposed to, perfectly. And then I wake up.