These days, multitrackers are designed as complete studio solutions rather than mere portable recording devices - even the most basic of modern machines now comes complete with a simple effects section, and more advanced models offer multi-channel effects processors and onboard dynamics processing such as compression and gating, to use both for general sound manipulation and mastering.
Many modern multitrackers, especially those aimed at guitarists, have started to include onboard amp simulators. Although not only designed for six-string strummers, more often than not they provide a useful selection of both guitar and bass amp and cabinet. Not only does this provide the performer with a vast array of sounds to choose from, it also does away with the painstaking process of miking real amps and speaker cabinets. As with most effects which are tailored for specific applications such as vocals, guitar, or drums, it's worthwhile taking a little time to experiment, for example by using guitar effects on vocals, or vice-versa, to achieve original and alternative sounds.