Looks like Calibre also holds a trademark: http://tmsearch.uspto.gov/bin/showfield?f=doc&state=4806:h6j...
There seems to be a high likelihood of confusion given that both are software products, but IANAL.
IANAL but I don't think the trademark is an issue. Might make it a bit hard to search for, though, when "calibre app" is dominated by calibre e-book software.
My understanding is that you can have overlap in trademarked names when it's in very different markets, but IANAL
Why on earth didn't they Google their own proposed name before releasing this? It's one thing to use the same name as another entity in a different field, but to rip-off a name that is already a well known software package too? They'll be lucky to make the first page of Google search results for their own name.
You can have different products using the same name so long as they're not in the same category.
So the guy who made this software isn't "taking someone else's name", he's using a name that isn't being used in that category (AFAIK).
Background: I once had to settle a trademark infringement case.
Usually that is taken as meaning categories such as 'beverages' vs 'cars'.
Trying to extend it to saying 'my three-wheeled car product called Ford Focus is in a different category to that four-wheeled one' would be unlikely to succeed
A recent example in the software domain was Python ( cloud services ) versus Python ( the language ). Python cloud services is now called Veber Cloud.
