The Zebra 2 from U-He is a software synth offering the sound and style of modular synthesizers without any of the visual clutter usually associated with such units. Available for download, it's compatible with most Windows and OS X platforms, works in 32- and 64-bit mode, and offers a multitude of sonic possibilities.
A matrix window in the middle of the GUI allows you to instantiate modules and filters, but much of the heavy lifting can be done within the oscillators themselves. For instance, each oscillator sports dual, drop-down effects menus which allow you to shape sound and character without applying external filters. Also, note the editor window at the bottom of the GUI; there you'll see a graphic representation of the oscillator which you can edit by hand, drawing in waveforms or harmonic content however you see fit. In this way, you can achieve both wave-table and additive synthesis, in addition to the subtractive styles of modular methodologies.
LFOs, envelopes, VCFs, and more are made possible through a panoply of different procedures, all of which can be daisy-chained. Thus, you can configure an assignable knob to target a parameter within the oscillator—a parameter which can then be modulated by an LFO in the matrix window, which can in turn be modified by any assignable characteristic in the global window, and so on, round and round, until the sound is as wild as you can possibly render it.
Another feature of the Zebra 2 is its streamlined user interface: if you're not using a module, it simply doesn't show up in the GUI. If you mute or bypass a module, it also disappears. This makes for an uncluttered visual experience. The preset menu is likewise divvied up into useful categories, and you can mark individual patches as "favorite" or "junk." Marking a setting as junk hides it from your view, though a right-click will bring it back. Lastly, should you choose to re-instantiate any module you've previously disengaged, it will appear exactly as you left it, instead of resetting back to its default. This too streamlines your workflow.