Pianoteq is a virtual instrument which you can install on your computer (PC/Mac). It can be used both in standalone mode and as an instrument plug-in in VST, AAX, and AudioUnits hosts.
Pianoteq's instruments are physically modelled and thus can simulate the playability and complex behaviour of real acoustic instruments. By omitting usage of samples, the file size is just a tiny fraction of that offered by other virtual instruments, perfect for use on any modern laptop.