There are many MIDI synthesizers out there. And each of them produces different sounds and gives different control capabilities. 74Hc595 have published pretty interesting MIDI device on GitHub. It is based on NXP LPC1114FN24 DIP-28 ARM Cortex-M0 microcontroller. It features four adjustable oscillators. Options include 2-pole low pass, high pass and bandpass filters, attack-release envelopes for modulation and other signal modulation capabilities. DAC output can reach 250kHz with 12-resolution.
Device has a MIDI input so it can accept commands from other devices like PC or keyboard.