Most tuners are hand-held and generally have an integrated mic and instrument input. Some even smaller credit card models are particularly favoured by wind and brass players, and sometimes incorporate a metronome.
Floor pedal tuners are popular with gigging guitarists as they integrate easily into any FX pedal setup and enable discreet tuning between songs.
19 rack tuners generally include advanced features and multiple input/output configurations. Wide, bright LED displays allow finer tuning steps to be displayed, and also have the advantage of being able to be read from across a stage or studio.
Clip-on tuners attach to the body of the instrument (typically the acoustic guitar headstock) and pick up sound vibrations by direct contact.
Tuners are also often integrated into other equipment such as electro-acoustic guitars and preamps, multi-FX units, guitar synths and even software plug-ins.