Here are some features Twitter DID NOT have when it began in 2006.

- Search
- Mentions
- Replies
- Retweets
- Lists
- Permalinks for tweets
- An algorithm

All of these features came when users demanded them.

The search function was actually built by folks who didn't work at Twitter. It was a service called Summize that eventually got acquired by Twitter and integrated into the service.

Retweets started when users began sharing other people's tweets by adding an "RT" before the text.