I read a post on Hey Milly's blog this week about the Apimac timer and classroom rotations which made me smile because I have used music forever as a transition tool within my room to signal tidying up, changing activities etc but this was done with a CD player initially and then I moved on to using my laptop and speakers. I was very excited to be able to download a timer which can manage this for me.
When I realised the Apimac timer was only Mac compatible I Googled free PC timers + alarms and was presented with several options. I have downloaded from http://www.timeleft.info/ which connects to www.netersoft.com/ and will trial this when I am working with children after the Easter holidays. It seems to have everything I would need in a classroom and additional features for me personally - it can be used as a countdown clock, reminder, clock, alarm clock, tray clock, stopwatch, timer, sticker and more. The main feature of TimeLeft is as a customizable reminder, which can show a message, play any format of music, or open a link, document, execute an application, turn off your monitor or shut down your PC.
I have tried this and works well as a timer but does not seem to have the music option in the free version despite that being stated under features. I returned to Google and have found an alternative at http://ptf.com/get/227809/ which I have downloaded and will try out.