Bobby George say's:
"When I play darts, I use this website for keeping the score!"
Free Scoreboard for 501 on this website.
You can set up a competition with a max of 7 players. Including: Outshots, High Scores, Averages and sound!
You can download the 501 Scoremaster program for Windows here or you can use the online version. Both with outshot hint & sound effect (one hundred and eeeeeeiiightieeee!!).