This category is for plugins related to SEO. There is experimental plugin jm_canonical (underscore means that it's experimental) that solves a lot of things, sometimes ones that are not related to canonical URLs. And you can't use it with metatag plugin.
e107 plugins - mostly made by somebody else and updated for new version of e107. Or too simple plugins without need separate category.
If plugin is in active development, it has separate the directory.
Fixed != Updated.
No php errors and everything seems to work, nothing more.