Synesthesia also has a number of practical applications, one of which is the use of 'intentional synesthesia' in technology.

Other forms of synesthesia have been reported, but little has been done to analyze them scientifically. There are at least 80 different types of synesthesia.

Evidence indicates that grapheme color synesthesia may be actually a case of ideasthesia. In other words, the vivid concurrent experiences of color may be induced by the concepts of graphemes and not by their sensory representations.

Individuals with grapheme-color synesthesia rarely claim that their sensations are problematic or unwanted. In some cases, individuals report useful effects, such as aid in memory or spelling of difficult words.

These experiences have led to the development of technologies intended to improve the retention and memory of graphemes by individuals without synesthesia. Computers, for instance, could use "artificial synesthesia" to color words and numbers to improve usability. A somewhat related example of "computer-aided synesthesia" is using letter coloring in a web browser to prevent IDN homograph attacks. (Someone with synesthesia can sometimes distinguish between barely different looking characters in a similar way.)

Hyperthymesia is the condition of possessing an extremely detailed autobiographical memory. People with hyperthymesia remember an abnormally vast number of their life experiences.

American neurobiologists Elizabeth Parker, Larry Cahill, and James McGaugh (2006) identified two defining characteristics of hyperthymesia: spending an excessive amount of time thinking about one's past, and displaying an extraordinary ability to recall specific events from one's past. The word "hyperthymesia" derives from Ancient Greek: "hyper-" ("excessive") and "thymesis" ("remembering").

Individuals with hyperthymesia can recall almost every day of their lives in near perfect detail, as well as public events that hold some personal significance to them. Those affected describe their memories as uncontrollable associations; when they encounter a date, they "see" a vivid depiction of that day in their heads. Recollection occurs without hesitation or conscious effort.

It is important to draw a distinction between those with hyperthymesia and those with other forms of exceptional memory, who generally use mnemonic or similar rehearsal strategies to memorize long strings of subjective information. Memories recalled by hyperthymestic individuals tend to be personal, autobiographical accounts of both significant and mundane events in their lives. This extensive and highly unusual memory does not derive from the use of mnemonic strategies; it is encoded involuntarily and retrieved automatically. Despite being able to remember the day of the week on which a particular date fell, hyperthymestics are not calendrical calculators like some people with autism or savant syndrome. Rather, hyperthymestic recall tends to be constrained to a person's lifetime and is believed to be a subconscious process.

Although hyperthymestics are not necessarily autistic, and likewise savants do not necessarily memorize autobiographical information, certain similarities exist between the two conditions. Like autistic savants, some individuals with hyperthymesia may also have an unusual and obsessive interest in dates. Russian psychologist Alexander Luria documented the famous case of mnemonist Solomon Shereshevsky, who was quite different from the first documented hyperthymestic known as AJ (real name Jill Price) in that Shereshevskii could memorize virtually unlimited amounts of information deliberately, while AJ could not – she could only remember autobiographical information (and events she had personally seen on the news or read about). In fact, she was not very good at memorizing anything at all, according to the study published in "Neurocase". Hyperthymestic individuals appear to have poorer than average memory for arbitrary information. Another striking parallel drawn between the two cases was that Shereshevsky exemplified an interesting case of synesthesia and it has been suggested that superior autobiographical memory is intimately tied to time-space synaesthesia.