Stats about the most used HTTP Server software
Short answer: the most common http server is Apache with a 34% share.
While scanning Web Servers for software version information, the system also collects a range of other interesting data about the servers included in the HTTP protocol transaction.
Most web servers provide some header fields which give the HTTP clients info or direction on what to do with the data being sent. Other fields may be informational only. Some of them bind the client to a strict policy.
You can browse a list of common http response headers found in the wild. This list includes both standard headers and server-specific headers which not all HTTP clients understands:
The system continuosly probes the Internet to find hosts which are running a Web Server.
Once one is found, it is queried to determine what kind of software it is running.
Current statistics are based on a sample of 84604 probed servers, gathered in the last 389 days.
This scan type is not based on website popularity nor on user submission; this grants the most realistic sample possible.
Please note that a "Web Server" is any program which obeys to the HTTP protocol.
This means not only your favorite news portal or weather forecast website, but also web services and, probably, your home router web interface.
(You should not open your router iterface to the Internet, anyway, unless you have a very good reason to do so)