Well, they've violated the terms of your license... To get back into compliance, they need to include the license text file. Email the person, and politely inform them of this... If they don't comply, then you may want to look into taking legal action.
For starters, is-a-geek.org has a lovely page:
If you wish to report a violation of our Acceptable Use Policy at a subdomain of is-a-geek.org, please contact our abuse department at
[email protected]. Please be certain to include the full URL of the suspected violation and a brief description, and we will respond to the issue as soon as possible.
Just to note, changing the name of the OS is something you probably want them to do if they modify the source code. You probably wouldn't want your project's name on a shitty version (This is why trademarks are a good thing, I hope you have trademarks on DexOS by now).
Not acknowledging another programmer's contribution to a code base is one of the worst sins a programmer can commit. Give him Hell for it.
I'm curious, how'd you find out about this in the first place? Furthermore, why did a guy named Christoph rename the project lukeos?