eLicense makes it possible to purchase a game and to pay using the credit card, or using money order, licensing the game online or manually through telephone or email and much more. It is in use on many, many computers with OOTP and TBCB and a lot of other products. Though it's easy to use, you might have some questions, for example regarding the un-licensing procedure which you have to go before you give your computer away or before you re-install your Windows.
A lot of information is available at Viatech's eLicense support page at
http://www.elicense.com/usersupport/el_faq.htm
In case of problems with the eLicense, please contact Viatech using their support form at
http://www.elicense.com/usersupport/supportreq.htm
Their eLicense Sales/Support hotline phone number is 508-647-0465 during business time.