VLC player is probably the most versatile media player out there today.
It supports almost every media file format you can think of and for that reason it is sort after on every platform, including mobile... including windows phone.
The VLC team have been hard at work developing a VLC player for windows phone, infact their efforts date as far back as more than a year ago now.
But they recently hit a milestone and have put out a beta version of the VLC app that is only available to those who registered as beta testers. If you didn't you are out of luck or maybe not.
Just like other windows phone beta apps (say for instance: whatsapp, facebook, BBM...), these users get first hand usage of new features in these apps and also have the responsibility of reporting bugs. Once these bugs are ironed out and the app is stable enough for public consumption, an update is issued to the public.
VLC dev team responsible for the WP app are still at the stage of ironing out instabilities and bugs, bugs that the beta testers submit.
So if you don't have the app, be patient as they hope to put out a public version before the end of the year (within the next 3weeks). This information according to a twitter response from one of the developers: Thomas Nigro:
So it looks like we will see the public release very soon or atleast before the year runs out.