1. Both are instant messenger technology.
2. Twitter limits the message to 140 characters. Most instant messengers do not have that limit.
3. Twitter added tables and index pointers to link things like who are the followers of whom and who does not want to be related to whom.
4. What else... really, technically, is the major difference between Twitter and any number of instant messenger services, all of which work just fine on mobile platforms of all sorts.
With another spending limit and sequester for 2nd year this company will again suffer the consequences of across the board budget cuts. Basic research grants are slashed and will be slashed again if Congress fails again to pass the budget or authorize spending limits. Right now, the plan is to slash across the board.