It seems like a long time since the year 2000. Much of the tech we take for granted didn't exist at the turn of the century, and yet technologies such as Twitter have become part and parcel of our everyday lives.

Here are the online technologies, sites and services that future historians will see as defining the last decade.

1. Napster

Napster wasn't around for very long - it launched in 1999 and was shuttered in 2001. The arrival of peer-to-peer file sharing of MP3 files blew the music business to smithereens. Napster got popular very fast and was sued by Metallica in April 2000. Had the record industry embraced it rather than fought it, file sharing might not have become the industry-killing concern it is today.

2. BitTorrent

BitTorrent wasn't designed for sharing music and movies: it was designed to speed up downloads. It just happened to be brilliant for sharing music and movies too, hoovering up bandwidth at such a rate that many ISPs now block or throttle it.

3. Facebook

Twitter gets the headlines, but Facebook gets the traffic: the Harvard-only social network expanded to cover other universities, then companies, then the whole world, and it now has over 350 million active users. It's the AOL of the 21st Century, but its ambitions don't stop there: its Facebook Connect acts as an electronic bouncer for a wide range of non-Facebook sites, including Yahoo ones.

4. AJAX

AJAX - Asynchronous JavaScript and XML - enables your web browser to get more data without refreshing the page, and it's the secret to browser-based applications that don't demand the installation of plugins. Google was the first big firm to really spot the potential of AJAX, using it to create services including Gmail and Google Maps and kicking off the web application explosion.

5. Blogger

Blogs were around before Blogger, but it took blogging from a niche pursuit to mainstream activity: Pyra Labs' 1999 invention had amassed hundreds of thousands of users during the early noughties by the time Google came waving its wallet in 2003. Its secret was simple: Blogging with Blogger was - and is - a doddle.

6. Twitter

In truth, Twitter is less popular than Facebook - but the speed at which Facebook is attempting to copy it shows how influential it's already become. Twitter's genius is twofold: you can follow people without getting their permission, which means a cat may look at a king, and there's a huge number of Twitter clients you can use to access the service. It's the email of social networking.