DS-404 is a sampler VSTi for Windows and MacOS, it's 16 way multi-timbral, each timbre has its 32 note polyphony. If your CPU is up to it therefore this thing is 512 voice polyphonic. It has an abundance of filter types, LFO's, looping, etc. and can load WAV, AIFF and its own 404 format sample banks.
Computer Music and Muon have announced their next free VSTi, to be included on the cover of Computer Music issue 50.