What are VST instruments and what program do I need for VST plugins?

VST stands for Virtual Studio Technology, a technology developed by Steinberg.  VST is an software interface that integrates audio synthesizers and effects with audio editors and hard-disk based recording systems.  So in layman's terms, VST allows you to digitize hardware synths and produce a slew of cool audio effects right on your computer!

VST uses Digital Signal Processing to emulate pricey audio recording and production hardware with cheaper (and more portable) software.  VST plugins at there most basic definition are add-ons to audio and midi editing programs.

A VST instrument is a specific type of VST plugin that is used to run a synth engine, rather than just produce some audio effect.

VST plugins are useless by themselves, they must be ran by an audio editor program. These programs are usually quite expensive, and are meant for audio production professionals. Nevertheless, here's a list of the top VST capable host programs.

Cubase 5 - Mac OS X or Windows

Cubase 5 comes with fully integrated new tools for working with loops, beats and vocals, such as LoopMash and VariAudio, combining with new composition features and the first VST3 convolution reverb to take musical creativity to new heights. With stunning innovations and additional enhancements that boost productivity and performance, Cubase 5 represents the absolute cutting edge in digital audio workstations. - Steinberg.net

Ableton Live - Mac OS X or Windows

"Ableton Live is about making music. When you're writing and composing, Live is quick and responsive. When you want to record and develop your ideas, Live has the depth and toolset for intricate production. It's got the features to take your DJ skills to the next level and it's stable and flexible on stage, whether you're playing in front of 10 or 10,000 people. However and wherever you make music, whatever music you make, Live will inspire you." - Ableton.com

Ardour - Mac OS X and Linux

A free (donations preferred) digital audio workstation for Mac OS X and Linux. A great way to mess around with MIDI and VST files for beginners.

FL Studio - Windows

"FL Studio is the most complete virtual studio currently available. It will play any sample file (wav), generator (softsynth), VSTi & DXi) or midi instrument you feed it." -flstudio.image-line.com

REAPER - Windows

"REAPER is a fully featured multitrack audio and MIDI recording, editing, processing, mixing, and mastering environment. REAPER is reasonably priced, requires no dongle, has no copy protection, and can be evaluated with full functionality." - reaper.fm

REAPER is free to download and try out, so it's another good way to try out VST files.

• Sonar by Roland
  
• Kore
• AudioMulch
• Bidule
• EnergyXT
• Max MSP

Free VST Hosts

Ardour and REAPER, both mentioned above, are free to download and try. The makers of the VST hosts would appreciate it if you paid, however. Use these to test out to see if VST instruments are right for you.