first of all, what is the "MC74HC244AN"? what can it be used for, motor/LED controller? and then, except for the first two items, what are some projects or circuits etc i could built with these ICs? Arduino or not related...
It wasn't quite as ubiquitous as the 555 but the 74LS244 was a very popular TTL buffer back in its day. It basically consists of eight (hence the OCTAL) amplifiers with a gain of 1 packaged in a single chip. You could 'turn it off' effectively disconnecting the outputs (hence the term 3-STATE). It was frequently used to 'buffer' or protect the output of expensive microprocessor chips as Mike has pointed out. The 74LS240 was pin-for-pin compatible but had an inverted output. The HC version that you have is a high speed CMOS version (hence the HS) in the middle of the part number whereas the LS version was a low-power schottky version. The prefix (MC) typically identifies the manufacturer and the letters at the end (AN) typically denote the package and other variations. Check out wikipedia for more on this (7400-series integrated circuits - Wikipedia).
Well it does wind up 'protecting' the microprocessor. It is essential in terms of what Mike is saying and has the added side effect of protecting the relatively expensive microprocessor at the same time.
When we switched from an 8085 system with buffer chips to the 68HC11 without them our students learned that the expensive way.