For many early networks, such as UUCPNET, FidoNet and BITNET, lists of machines that were open relays were a core part of those networks.
Australian Open | French Open | The Globe and Mail | Daily Mail | Relay race | Open University | open source | U.S. Open | Royal Mail | Wacken Open Air | The Open Championship | U.S. Open (tennis) | Butterfield Overland Mail | All England Open Badminton Championships | U.S. Open (golf) | Open Source | Open-pit mining | Mail | 2006 Australian Open | The Courier-Mail | Open Software Foundation | men's 4×400 m relay | Indira Gandhi National Open University | Birmingham Mail | Athletics at the 2008 Summer Olympics – Men's 4 × 400 metres relay | Lamar Hunt U.S. Open Cup | 2005 Australian Open – Men's Singles | U.S. Women's Open | open access | Mail order |