My company and I have used electronic signatures on documents with the last few tech companies I’ve worked with (including Microsoft) and in buying/selling two homes now. The Electronic Signatures in Global and National Commerce Act (ESIGN) of 2000 ensures the legality. When I worked at Microsoft our contractor agreements were all run via digital signatures using EchoSign and DocuSign.
DocuSign and EchoSign (now owned by Adobe) are two of the most popular electronic signature options. EchoSign gives five free signatures per month under their free trial. SignNow is an iPhone app. It’s quite convenient to be able to receive, sign, and send back out legal documents straight from the mobile phone.