The question, as well as previous answers, are as of this writing 15 years old. Not suprisingly the software landscape has changed, and all links in the older answers are either dead or going to a generic page not containing any relevant information. As this question still is a top result on search engines it might benefit from some updated information:
Some free projects based on forks made before Reflector went proprietary:
Things may have changed again by the time you read this.