The simulation is carried out using ngspice using the mixed-mode xspice capabilities. The digital section is synthesized using yosys that can then be bridged to/from the analog section.
The Schematics are created using xschem, which also serves as the simulation framework.
The simulation output can then be viewed in both analog and digital domain.
Digital waveforms displayed using GTKWave
Analog waveforms displayed using Gnuplot in interactive mode.