If you're looking for another free service that's kinda in between Tag Manager and Segment.io, we built "Add This Script" (https://www.addthisscript.com/) that lets you choose from more than just analytics scripts so you can include jQuery or Facebook widgets and manage that all in one place. We add new services every week or so.

We're also working on some dependency management stuff so you can include jQuery UI and it'll automatically pull in jQuery, for example.