Book Designer is a Great tool for Creating and Editing files and converting them to LRF
https://www.mobileread.com/forums/showthread.php?t=11786
I Prefer Not to use Calibre. Automatic converters never Sit well with me.
another tool which is nice is
https://www.mobileread.com/forums/showthread.php?t=28313 it basically just a bunch of macros in microsoft word which make it easier to create Ebooks its good, but not nearly as good as Book Designer (if this had an Element Browser like Book Designer i might use it more) This has the Option of converting to Epub, but i tried it last night and didnt get it to work so....