O artigo da wikipedia Push technology pode ser um excelente ponto de partida:
Synchronous conferencing and instant
messaging are typical examples of push
services. Chat messages and sometimes
files are pushed to the user as soon
as they are received by the messaging
service. Both decentralised
peer-to-peer programs (such as WASTE)
and centralised programs (such as IRC
or XMPP) allow pushing files, which
means the sender initiates the data
transfer rather than the recipient.
Email is also a push system: the SMTP
protocol on which it is based is a
push protocol (see Push e-mail).
However, the last step —from mail
server to desktop computer— typically
uses a pull protocol like POP3 or
IMAP. Modern e-mail clients make this
step seem instantaneous by repeatedly
polling the mail server, frequently
checking it for new mail. The IMAP
protocol includes the IDLE command,
which allows the server to tell the
client when new messages arrive. The
original BlackBerry was the first
popular example of push technology for
email in a wireless context.
Another popular type of Internet push
technology was PointCast Network,
which gained popularity in the 1990s.
It delivered news and stock market
data. Both Netscape and Microsoft
integrated it into their software at
the height of the browser wars, but it
later faded away and was replaced in
the 2000s with RSS (a pull
technology).
Other uses are push enabled web
applications including market data
distribution (stock tickers), online
chat/messaging systems (webchat),
auctions, online betting and gaming,
sport results, monitoring consoles and
sensor network monitoring.
O artigo acima contém muitos links que não foram duplicados aqui.