I2C
and TWI
should be synonyms, they are the same thing with a different non patented name
Source: http://en.wikipedia.org/wiki/I%C2%B2C#Derivative_technologies
TWI (Two Wire Interface) or TWSI (Two-Wire Serial Interface) is essentially the same bus implemented on various system-on-chip processors from Atmel and other vendors.[9] Vendors use the name TWI, even though I²C is not a registered trademark. Trademark protection only exists for the respective logo (See upper right corner) and patents on I²C have now lapsed.
There is also a 555
and 555timer
tag, these should either be merged or synonyms.