BassMidi VSTi

BassMidi VSTi is a featherweight audio plugin that provides you with a comprehensive audio synthesizer and various MIDI controllers for processing and for simulating traditional recording processes.

Portable VST MIDI synthesizer based on the BassMidi audio libraries

As with all VST (short for Virtual Studio Technology) plugins, it requires the presence of a VST host or a DAW (Digital Audio Workstation), as well as some SF2 or SFZ soundfonts in order to work.
This is probably the best time to point out that BassMidi VSTi works on both x86 and x64 systems and should be to do so with the vast majority of VST hosts out there, but it has been tested mainly on SAVIHost, VSTHost, Reaper, Cubase LE Elements 8 and Soundfont Midi Player. Before we go even further, please note that the usage of host bridges is not recommended.

Straightforward and fairly well-documented deployment procedure

As mentioned before, you need to make sure that a VST Host is installed on your computer's system. Start off by copying the Bass.dll and Bassmidi.dll components to the same directory as BassMidiVsti.dll.
Copying BassMidiVsti.vstxml and Bassflac.dll are both optional, as the formers can be used for simplifying the customization process while the latter is only required if you intend on using FLAC compressed SFZ files.
It is worth mentioning that BassMidi VSTi is perfectly capable of supporting up to five different stacked soundfonts, twelve reverb or chorus effect types, and fourteen parameters for options that are not Midi accessible.

Widely-accessible and lightweight VST plugin for Windows

Taking everything into account, BassMidi VSTi is a lightweight and very accessible plugin that can be deployed and used without much effort on most Windows platforms out there.
The plugin packs a simple main editor interface, supports a fair number of stacked soundfonts, audio effects, and parameter controllers, and it also comes with a decent documentation section, meant to help even the most novice of users find their way around it.