Captive Portal

[Is there a captive portal that keeps the MAC addresses of people that connect on our wireless Internet in some database?]

I just started working in a company that have a free wireless network. Everyone who has a laptop or a mobile phone should be able to connect without a fee. We don't ask for any authentication.
Our cisco wireless controller writes a list of users that are connected on our APs every 5 seconds, but it keeps no permanent record in any database... My job is to get that statistic. I used to write those data into database by hand but it takes me too much time and it is humiliating...

I want to find an answer that will automatically keep statistic .

Is there a captive portal that keeps the MAC addresses of people that connect on our wireless Internet in some database?

Please help!

There may be somewhere, but m0n0wall will not.  However, you can do some external logging.  Either RADIUS or syslog will give you what you need.  The choice would be based on what you have more familiarity with...