Another thing that I don't think has been mentioned is "open" stations, i.e. stations without ticket barriers, where passengers (and everyone else for that matter, such as railway enthusiasts and people meeting passengers or seeing them off) could enter and leave the station freely.
Under BR in the 1980s and early 90s, permanently staffed ticket barriers were gradually phased out in favour of on-train ticket checks, so by the time of privatisation the newly franchised train operators inherited an almost completely "open" system, but since that time the powers-that-be have decided that on-train checks alone are not entirely foolproof and that barriers are needed to prevent fare evasion after all. The question of whether this is really necessary, and whether the open station system could have been made to work, has probably already been discussed to death in numerous other threads on here.
Most of mainland Europe changed to open stations in the 1960s and 70s, and in many countries (e.g. Belgium, Germany, Austria, Switzerland, the Czech Republic) they remain the norm to this day. A few countries such as France, Italy and the Netherlands have reverted to barriered stations to some extent in recent years, though. Netherlands Railways has gated most of its major stations, and many smaller stations in the major conurbations, as part of its OV-Chipkaart smartcard/contactless ticketing system.