ODT is an open standard, i.e. there is a clearly published description of how files in this format need to look like it (as opposed to the Microsoft Word standard which is controlled by Microsoft).
If you wish to try out ODT, you can download a free copy of open-office unless you own a PowerPC mac, then you would need to use NeoOffice.
Both these programmes exist now in version 3 which is far superior to version 2. There has been some weird behavior in version 2 of open-office when converting text files, which seems to have been fixed in version 3.