[ant_thomas]

I would simply like to know what the reason was to develop TVheadend?
What exactly was the target?
Should it be a replacement for VDR?
Are there any advantages over VDR, or are these programs not comparable?
Does it maybe fit better to XBMC?

Any explanation welcome. I just want to understand the meaning.

As Dushmaniac said, TVHeadend is just an alternative to VDR, probably the recommended backend due to the level of support it currently has from the XBMC community.

I use VDR but that is a personal preference. I'd say TVHeadend is easier to setup but I feel VDR is more powerful and flexible once you get used to how it works, but it can be a bit of a learning curve if you've not got a good handle on linux and DVB/TV things with linux. There's nothing like the web interface that TVHeadend has (afaik) for VDR. I have definitely had to do a lot of reading and asked a lot of questions on various forums and IRC channels to get my setup as it is now.