I have been using HELM control panel on my Windows servers from start. Today i was moving one of my windows server from ThePlanet to Softlayer. The HELM license used in the server was expired and i was not able to upgrade, they charge $225 to get 1 year upgrade. One of the reseller (Rubel – if you ever visited HELM forum, you will know him, he is very helpful member of the forum.) offered upgrade for $125 so i asked HELM to push the control panel to his account. I got reply from SWSoft saying the license transferred, then only i know HELM is now owned by Plesk.
Plesk is Linux control panel, i used it on my first web site. But i like Cpanel lot better. Plesk have windows control panel too, but HELM was much popular for windows. May be they sold out because Cpanel is working for Windows control panel, once Windows version of cpanel released, many will switch to Cpanel and many data centers will bundle it with server offerings as Cpanel have strong market share in Linux control panels. Almost 90% of web hosts use cpanel control panel.