Why not Twitter have more options like following

Today When I am using twitter all message are visible to every one who ever follows me.

Why cant I categorize my followers as different groups such as co-worker ,School Friends,all others,

When I post some thing if want to show to only my school friends but not for all and they can re tweet my posting to their friends at the end I should see who is reading this message I should see who read the message such as people who received my tweet from my school friend.

If i want to post short message to specific person I should be able to post this message can be only seen by that person if that person follows me.

it should also have features like buzz had which means it should look like micro email with micro group discussions

person to person message like Orkut has presently scrap person to person communication
person to group message i did not find any thing like
person to any one who ever follows Twitter.
on top of all three above it should have continuity like google Buzz has where people can edit and add the comment