How can I get the IP address, MAC address, etc. of a user connected to a Wi-Fi hotspot? ( Using Karbonn A21 Phone running Android 4.0.4 with minor changes to the skin)
Take a look at Network Discovery1 -- it lists all devices within the same network, together with some details on them, as e.g. IP, MAC address, available services:
Other port scanners will do as well.
1: This app is no longer available on Play Store.
Another alternative is Wifi Watch.