Cat 5e = un-screened unshielded twisted pair. Good for 100Mhz and can run GigE
Cat 6 = un-screened unshielded twisted pair. Good for 250Mhz (i think) and can do GigE
Cat 6a = screened unshielded twisted pair. Doubles bandwidth but i think is still only good for GigE but be able to do 10GigE
Cat 7 = screened shielded twisted pair. So thats means there is an overall screening as well as each pair has it's own screening. Good for somewhere around 700Mhz i think and can blast 10GigE down it.

Summary, it really doesn't have a place in many enviroment except for the data center or maybe tie cables from the patch panel to server rack or something like that.

PDL made a product called Lexcom for homes. It ran what is essentially Cat 7 cable just without the standard pair colourings. It can run audio, video, data and phone but in practice was rubbish and VERY expensive.