failover DNS

I want to have a failover DNS, where, 1 entry can point to 2 different ip address. But at one time, only point to 1 primary server.
And if the primary server down or not available, the other server will take over and the dns can automatically change the dns entry to point to the failover server.

1. I want to know whether simplefailover can do or not?
2. if yes, what os platform should i use to install it?
3. is it free software?
4. how about maintenance. is it easy to maintain?

hope all the experts out there can help me. I really appreciate it. Thank you.