Touch pens
In addition to fingers, mobile devices often support touchscreen pens / touch screen stylus / capacitance stylus.
These allow you to activate the interface without actually touching it, and allows natural handwriting as input for notes, signatures, etc.
It also makes it easier to see the screen for precise selection.
Digital Stylus
These are “active stylus” systems that are more advanced than the passive capacitative touch pens. They work by communicating independently with the device, and therefore allow for pressure sensitivity, programmable buttons, etc.
Unlike capacitance stylus, an active stylus must be compatible with the technology group → Apple iPads must use Apple Pencils.
Drawing pads
You can also add external drawing pads. These are active styluses combined with an external Digitizer. Unlike the digitial stylus above, these are third-party devices that support many operating systems.
Trackpads
Track pads replace a mouse and are common on laptops. There is an option to have external trackpads that connect over Bluetooth, which allow the same functionality of a laptop and can include multi-press and action configuration.
Some laptops have the option to disable the trackpad with a specific FN-key
Headsets
Headsets allow for hands free audio: they might use USB, 3.5 mm TRRS (tip-ring-ring-sleeve) connectors - analog audio jacks -, Bluetooth, or lightning port for iPhones.
Speakers
the speakers in phones and laptops might be weak. The option is to use external speakers, often battery powered and connected via Bluetooth.
Camera / webcam
Internal or external; commonly external on desktops.
Docking stations
A docking station uses an external keyboard and mouse and extends existing laptop interfaces. They add additional functionality, remove cable issues. Some docks might even provide adapter cards to expand the laptop itself.
Port replicator
Similar to a docking station, but connected via USB. They don’t tend to have the option for expansion cards.
They generally allow a single USB connection that then give access to all the other ports of the replicator itself (dongles are like portable replicators)