Can I oppose a Community Trademark application with my brand?

I am aware of your query which is all except trivial and I would like to complete the explanation of Alexander.
In Europe we acquired the trademark only by registration, with the exception of the well-known mark. And only a registered trademark is (judicially) enforceable before the courts as only a registered trademark can be infringed legally speaking.
However, registration is not systematically required to oppose against the registration of a later trademark, in particular a Community trade mark (CTM).

Namely I understand that you use for three years an unregistered mark to designate your software developer activity, particularly in the UK.
I also understand that a competing French company had recently filed a CTM application for a close marks - visually and phonetically speaking - before OHIM.

In my opinion, you can attempt to oppose the registration of the later trade mark before OHIM by invoking prior use of your non-registered sign (Art. 8, § 4 of the Regulation on the Brand Community), since:

1 / under the law of the member state that is applicable to this sign - in this case, English law - that sign gives you a right to object to the use of a later trademark,
2 / your previous non-registered sign has a scope that is not purely local,
3/ the publication of the post competing trademark was made less than three
months.
Of course, it is still necessary that these three conditions are properly met...

Please don't hesitate to revert to me should you need further details.
Sincerely yours,

Simon

You should contact a trademark attorney in Europe - an attorney in any EU country should suffice. Under U.S. law, you could have a case because you acquire rights in a mark in the U.S. merely by using it (marking goods or advertising services actually offered and sold or rendered in U.S. Commerce) and a registration is not necessary to enforce those rights, though enforcement is much easier with the registration. UK might offer more usage right than other EU countries but I think generally speaking, registration in the EU and EU countries is really required to attain and enforce trademark or service mark rights.