Some beamer themes provide footlines -- and some do not.
Now, if one wants to have a footline, he is restricted to the (outer) themes providing them or loads multiple themes. On top of that, these provided footlines are only configurable by redefining them as a whole, which is quite uncomfortable and yields many lines of additional code.
hackthefootline is a package taking over, defining and redefining different footlines, so they can be configured using key-value syntax. Also, it is possible (but not recommended as it might distract your audience) to switch between different footline types during a presentation.
hackthefootline depends on the packages ifthen and pgfkeys and -- obviously -- on the beamer class.
Additional sophisticated features included also require appendixnumberbeamer (only when using beamer v3.48 and older), etoolbox, calc and numprint, but these four dependencies can be resolved by passing some options to the hackthefootline package.
This work is licensed under the LPPL 1.3c or any later version.