J. River Media Center includes several servers.
Library Server, formerly called Media Server, can serve a media collection on one PC, so it can be played with another copy of MC on another PC anywhere on the Internet.
Tivo Server can serve MC's library to a TiVo.
MC14 terminology for UPnP was changed to DLNA / UPnP. DLNA and UPnP are similar but not identical protocols.
Remote Server is a small web server built into MC, and allows MC to be controlled from a web browser running on another PC. MC15 replaced Remote Server with the more graphical WebRemote.
The first three servers are located in MC's tree, under Services and Plug-ins, and that is where they are configured. In MC15, configuration moved to Options/Network.
MC14 introduced a Web Service Interface.
MC14's DLNA also provides some server options, and can be used with both software and hardware from many sources.
Several third party applications use MC interfaces to control the player. See Remotes for more information.
Media Server is a small program that runs in the background. It can start up other servers when they are needed. It appears in the lower right corner of the desktop, and it will show up in the task manager as Media Center. It was introduced in MC12.
Several older servers have been retired and replaced.
Remote Server was replaced with the more graphical WebRemote in MC15.
UPnP Server was folded into the DLNA Server in MC15.