Online banking is one way to send money to someone without mailing a check. Many banks also have online options to send money to anyone with an email address. But there are two other services that have apps which will work on and from your phone or tablet (Android or Apple) as well as from your computer: PayPal and Google Wallet, each of allow you to send money for free to anyone who has an email address. One word of caution with Google Wallet: You probably want to go into its Settings and un-check the box that lets Google Wallet notify you of deals near you.
Play Links: http://tinyurl.com/d95uldf (PayPal) and http://tinyurl.com/cbvqfet (Google Wallet)
Apple Links: http://tinyurl.com/mx8qhha (PayPal) and http://tinyurl.com/oxyjjzj (Google Wallet)