Patrik. Definitely not a common house fly. In fact something rather interesting which eats ordinary flies!
A species of Robber Fly (Asilidae family). Looks rather similar to Neoitamus cyanrus to me; but they are difficult to fully identify and need shots from several angles.
Hoverfly Orgy
Carrying on from Randy's beetles having fun. Here is a scene which I witnessed yesterday; although I have seen this behaviour once previously.
This Eristalis interruptus female was feeding when she was pounced upon by 4 males. They all hovered just over her thorax, with quite a bit of 'buzzing' then dropped lower to touch her thorax.
But she wasn't in the mood and eventually flew away. I have yet to take any photos of this species actually mating.