There must be a version for Ubuntu Linux also
Why ? I thought ext4 didn't need defragging ?
[/joke]
Piriform won't do this. Linux is used in 1% of computers. Programming for Linux means you'll never get any money from it.
And even if they did, they should make their program open-source - and I don't think they want to do that.
Linux has an architecture where it does not need to be defragmented. No need for a Linux version.