Is there any FREE plugin that works just like Turnitin with Moodle 2.6+?
No, there is not a FREE plugin that works like TurnItIn with Moodle 2.6+
I think its fairly clear what, exactly, was being said 'no' to.
To give a fuller explanation, if one is really needed:
Plagiarism software isn't written for Moodle, its an external service. The plagiarism plugins available for Moodle do not do the plagiarism checking, they link to those external services. Those plugins are free - but the services they link to are (usually) not. And a list of those available is one click away in the plugins database for anyone who wants to look - https://moodle.org/plugins/browse.php?list=category&id=35
And as for 'like TurnItIn' - despite the bad press TII has had recently for various reasons - I'm not sure there is anything like TII even as an external service. The range of services, alongside the plagiarism checking (Grademark, etc), the range of material they do that checking against and the market takeup would suggest probably not.
As for the questions put
'that no free software is available?' well, there's Moodle for a start, Linux, Libre Office, Firefox, Gimp.............
'that nothing like TurnIt-in is available?' Personal opinion - no nothing like TII is available: There may be competition in the purely plagiarism area, but TII offers more than that.
'that plagiarism software is not available for 2.6 Moodle?' As noted above, plagiarism software itself isn't written specifically for Moodle, although plugins that link to external plagiarism services are.
But none of these are what was asked:
'Is there a free plugin that works just like TurnItIn for Moodle2.6+' - No.