After years of waiting, we finally get to see Microsoft’s latest addition to the mobile operating systems world: Windows Phone 7. They have put a lot of work into it, and written it from scratch with future customer demands in mind, and just like Windows 7, it looks and works pretty damn well.

The interface is especially well thought out, and it’s so easy to navigate it and work with the OS after you learn the basics, that you’ll actually find the Android interface hard to use. The iPhone’s interface can certainly compare to it in terms of simplicity, but Windows Phone 7 has a sense of elegance and uniqueness, which a lot of people will prefer over practical simplicity.

Windows Phone 7 is also up to date with the app revolution: there are already thousands of apps on the new and improved Marketplace, and the database is growing every day. Developers actually say it’s easier to create apps for this OS than for Android, which really says a lot about it. If you want to buy or already got a Windows Phone 7 device, you’ll definitely want to install some apps. With that in mind, here’s a selection of a few apps that you simply must have on a new WP7 smartphone:

Youtube. YouTube is one of the most popular websites online, with over 1 billion monthly views, and you’re most probably visiting it, too, if only from time to time. Well, Windows Phone 7 doesn’t have Flash support yet, so you can’t use the browser to view the site. That’s why you need a third party app and the “YouTube” app is the best one out there. It actually comes pre-installed on many Windows Phone 7 devices, but if you don’t have it, just download it from the marketplace.

Adobe Reader. If you think you’ll ever need to open a PDF document (and I’m sure you will), having Adobe Reader installed is a must. The app works pretty well on Windows Phone 7, and you can open any PDF files you want without any problems.

Twitter. Twitter, the largest micro-blogging social network, has released their official app for Windows Phone 7 pretty quickly, and if you’re using their service and just bought a new WP7 smartphone, you should definitely download and install it. You can then use all of the features you get on Twitter: threaded replies, photo/video uploading, following people, and much more.

Facebook. Facebook is being used by over 400 million people worldwide, and if you have a profile on this social network, then a client app for your smartphone is simply a must have. The official app from Facebook has been released since Windows Phone 7 has been announced, and it ships with most of the phones, but if you don’t have it installed, you can easily get it on the market.

Flixster. If you like movies or cinemas and want to keep up to date with the latest releases and theater show times, you’ll definitely want to have Flixster on your phone. Not only it is free, but it allows you to find the best show times, read critics and viewer reviews of any movies, discuss a movie you’ve just seen with other people, and much more.

Windows Phone 7 is certainly a great platform and if Microsoft is serious about getting back to the mobile OS sector, they can easily make it a very competitive product that can satisfy everyone, from business users to regular people who use their phone for everyday tasks. The apps marketplace for WP7 is growing bigger every day, and if you just got a smartphone running the new OS, be sure to check out at least some of the above apps.