Piotr "Habib" Pyrzanowski has released keFIR, a zero latency, mono, FIR filter plug-in, based on impulse responses loaded from wave files. Filter length can be adjusted to maximum of 8K taps. It has a "mix" knob for mixing input with output, "gain" knob for setting output volume level, "length" knob for setting filter length.
Its purpose is to apply cabinet emulation on a guitar signal, with no latency, so it could be used for live performance or with direct input recording, etc. Beside that, it can process almost any impulse response to any source signal, so there's no usage limitation.
keFIR is available as a VST effect plug-in for Windows and it is free (Donationware).