This site is not an LU site, nor is it associated with LU.
Clive's UndergrounD Line Guides are a series of files describing the London Underground system and the independent railways of the London area - the Docklands Light Railway and the Croydon Tramlink (neither is a part of London Transport, though the DLR used to be). Each line is covered in a single file, all in the same format.
The following arrangement by type of line and date of opening may also be of use to readers:
("Date of opening" here refers to the line as a significant entity, not necessarily to the first section of the line to carry trains.)