An answer to this question on QSL cards refers to something called Logbook Of The World or LOTW.
What is LOTW? What is its history?
What problem does LOTW solve? (that isn't solved by plain QSL cards or email confirmation)?
Why does taking part in LOTW seem so complex (digital certificates and signatures with custom library code, etc.)?
To add to Jim's answer, one of the goals of Logbook of the World is to be a secure system (reference). This presumably was necessary because contacts with some DXCC entities or other stations are very rare, and such contacts are very sought-after by many people. The American Radio Relay League's rules about certificates follow security practices that are commonly used for secure computerized transactions over the internet. The rules can be cumbersome because the League wants proof that that the person requesting the certificate is actually the operator in charge of the call sign.
Other similar services exist where operators upload their logs, but they have different goals. eQSL is designed to be easy to use, and to be like paper QSL cards in that users can share a graphic picture; however it's not as secure as LOTW, and so the ARRL doesn't accept eQSL confirmations for DXCC awards. (Also surely the ARRL is somewhat biased towards their own system.) Club Log was designed as an electronic system to allow people to check if they are in the log of a DX station, and has since expanded to be a computerized toolkit for DXers.
LOTW is a service provide by the American Radio Relay League or ARRL. It started in 2003. it allows a secure upload of your ham radio contacts to an online database. By matching your records with those turned in by the people you contacted the contact can be verified in minutes instead of months or even years which is how long it took with paper QSL cards.
There are other groups that offer similar services, like eQSL or club log, LOTW is the most popular.
Currently over 1 billion contacts have been recorded in LOTW.
LOTW records can qualify you for several award such as Worked all States (WAS) for making a contact in each of the 50 US states, or DXCC for making 100 contacts with different entities across the world. Most entities are countries, but some countries have several entities under their jurisdiction. For example besides the US mainland there is Alaska, Hawaii, the US virgin Islands, Puerto Rico, Guam, and American Samoa all of which count as separate entities.
Many users upload their data to LOTW world after every day they operate. Other many do so only occasionally and of course not all ham radio operators even use LOTW. I recently made a contact with a person in the Falkland Islands. This would have been another country toward my DXCC, but he does not use LOTW or even QSL Bureaus. I will at some point send him a QSL card, but I may or may not get one back from him and it will not be soon.
