Apex PBM Soccer was one of the popular in United Kingdom soccer manager games that were played via post (yes, it was in pre-Internet era) and allowed people from different parts of the world (well, UK mostly, international letter were not fast enough) to compete against each other in computer simulation of soccer management even without a computer. It was time wasting method, it was definately not cheap (from 1 to few pounds per round!), but at that that it was the best way to actually join multiplayer soccer manager game.
Apex PBM Soccer had very simple rules that were described in small booklet, but the rules were actually logical and well developed. Each week users had to send them the teamsheet with team selection, formation and tactics. Also simple stadium expansions orders were available. At the beginning of the game each user was given squad full of exactly the same players (with average skills), but there was a nice twist - you could name your players and decide their positions. What it the twist? The players already had age and skills set, but you could choose if the young promising 19-year-old player will be a goalkeeper or future top scorer, the 26-year-old universal player with average skills be your playmaker or defender, etc. And that was the best part of Apex PBM Soccer - tiny little things that could make a big difference.
Among other PBM games that were available at that time Apex was rather simple, but well developed.