This type of thing maybe?

http://www.smithfrancistools.co.uk/Default.asp?Page=41

I find them very time consuming and they make a right mess of the
surface. Fine for packing cases, but I wouldn't use them on floorboards.

Yup - tried one - took it straight back to the shop. The tool has to
chew through the surface to get at the nail - as you say, fine on
packing cases.

In older properties you may find you have cut nails rather than modern
round or oval wire nails, and these old nails may be much more
difficult to shift.

My technique is to put 6mm spax screws in with an impact driver
(missing a joist of course), all the way through the board, with the
screwhead standing just proud of the board, at the point I want to
lift it. Then use a crowbar hooked under the screw head, and bearing
on a bit of scrap timber. Enables me to lift stubborn boards with only
a screw hole as damage.