I want to try the app on my nokia lumia 520, my phone is dev unlocked, but i can't find the Nokia Beamer xap. Can anyone help me?
Dev unlock only allows you to sideload apps that use tier 3 capabilities (which is the same as most of the apps published in the store), so you gain nothing in terms of "power", just the ability to sideload homemade apps.
We can't just pull decrypted XAPs from our phones... You need interop unlock for that (and possibly more), and so far that's only achieved on Samsung phones. Your best chance is to get someone with an unlocked Samsung device to install Beamer by using the proxy trick, then posting the XAP so you can sideload. But be aware this can potentially create new issues - it's an OEM app, so it probably uses capabilities not covered by dev unlock (which means you won't be able to sideload).
Or you can just try the proxy trick yourself. Change the device model to something with 1GB and it should be available for download.