Twitter is a social networking and micro-blogging service that enables its users to send and read other users' updates known as tweets. Tweets are text-based posts of up to 140 bytes in length. Updates are displayed on the user's profile page and delivered to other users who have signed up to receive them. Senders can restrict delivery to those in their circle of friends (delivery to everyone being the default). Users can send and receive updates via the Twitter website, SMS, RSS (receive only), or through applications such as Tweetie, Twitterrific, Twitterfon, TweetDeck and Feedalizr. The service is free to use over the web, but using SMS may incur phone services provider fees.
Instagram is an online photo-sharing and social networking service that enables its users to take pictures, apply digital filters to them, and share them on a variety of social networking services, such as Facebook or Twitter. A distinctive feature is that it confines photos to a square shape, similar to Kodak Instamatic and Polaroid images, in contrast to the 16:9 aspect ratio now typically used by mobile device cameras.