All of these mods are for website integration for RetroAchievements, which is a website where people play and rank themselves against others by playing older games typically. The community is very welcoming and caters to players of all different kinds. The RetroAchievements mod is for those who just want to beat the game as any character, more so it's just for fun.Where as, the other three are for more specific and harder challenges that the typical player may or may not actually want to do. Thus, they are divided into three subsets of achievements that are all tracked differently. Someone may not want to collect every item on a hardcore player so completionist achievements and hardcore play achievements are separated. Also, the World Achievements is for people who want to play all of Terraria's secret seeds. I hope this helps and if you want to try out RetroAchievements you can do so here: https://retroachievements.org/ Signing up is free and there should be instructions for playing any of the older games that are supported.