They might not have been there at the start of day one, but by the end a number of "flagship" apps hit the Windows Phone 7 Marketplace.

Those who've picked up a new HTC, LG or Samsung device powered by Microsoft's new operating system can now watch YouTube videos, tweet on the official Twitter app and chat with their mates via a Windows Live Messenger app.

If you are giddy by the excitement, then brace yourself for the news that Adobe has released Acrobat Reader for Windows Phone 7, allowing you to read pdf files on the go. Whoop!

All the above apps are free.

Sadly the YouTube app is only half the story, as it only allows you to view content on YouTube's mobile site and doesn't support embedded YouTube content, like the sorts of videos you'll find on lots of websites.

Others now in the Marketplace include Shazam and GoVoice - a Google Voice app costing a couple of quid.

The new high-profile additions add to the bevy of big names like Facebook, Ebay and Foursquare, all of which are already available.

Which apps have you downloaded? Let us know in the comments below...

Windows Phone 7 - what apps did we get?