Straightliner (approximately $120) from Robin Schmidt's Music Engineering Tools (rs-met.com) is a pure subtractive, virtual analog synthesizer that, refreshingly, makes no attempt to emulate a hardware synth's control panel. All of its settings are graphical or numerical and are logically organized on a single screen. A few minutes with the 6-page manual, and you're on your way. Beyond ease of use and a great sound, several things set this synth apart.
Straightliner's signal path starts with four oscillators into which you can load any single-cycle mono or stereo waveform in FLAC or WAV format (the usual waveforms are provided to get you started). The whole signal path is stereo, so stereo waveforms do add breadth. The oscillators also support microtuning and import scales in the Scala format. The oscillators are mixed and fed into a multimode resonant filter that offers the typical configurations along with allpass and shelving filters, a morphing lowpass-to-bandpass-to-highpass filter, and a carefully modeled emulation of the 4-pole Moog ladder filter. A handy TwoStages button instantly stacks two of the chosen filter types in series.
For control, you get two breakpoint envelope generators (EGs) that loop and sync to tempo. One EG is dedicated to the output amp and the other to filter cutoff. Both offer variable Velocity and keyboard tracking. All modules have their own preset load-and-save capability and come with a smattering of useful presets. You also get a categorized library of full-synth presets. Straightliner is easy on the CPU and excels at analog-modeled sounds (see Web Clip 1). Grab the free, time-limited demo and give it a listen.