Most of the amp simulation packages available for guitarists offer a few bass amps among the models, but software specifically designed for bass is a rarer beast.
IK Multimedia's Ampeg SVX is one option, as is the latest addition to the genre: the Markbass Mark Studio 1, software that is designed to replicate the sound of the Italian company's bass amplification. It is available for both OSX and Windows in RTAS/AU/VST plug-in formats and can also be used in standalone mode.
What you get are models of three amp heads – the TA 501, R 500 and Classic 300 – coupled with six different speaker cabs. Tools to tailor the sound include six virtual microphones and one preset two-mic combination. There's also a fully adjustable compressor in the signal chain.
The 64 factory presets offer a wealth of solid bass tones suitable for a range of musical genres, with plenty more available by tweaking amp controls, positioning the virtual mics (even on the rear port of ported cabs) and adding the very effective room ambience.
The compressor can keep dynamics nicely under control, and the ability to mix the direct dry sound with the processed offers real versatility.