I have that habit of selecting text snippets while I read (like adding breakpoints every few lines), but still I find it quite helpful when I can share a given snippet in an article by selecting it and sharing it through a popup.
I found the WP Selected Text Sharer in the repo and it looks pretty close to what I need, however it hasn’t been maintained for a while (more than 3 years). I have contacted the plugin author and he mentioned that he’d like to rewrite it one day, so I forked it into a simplified version with few bugs cleared named DX Share Selection.
It’s quite neat and includes several features by default, such as sharing to popular social networks like Twitter and Facebook, searching a selected snippet in the blog or Wikipedia (or Google) and it parses it’s own simple template language that allows for adding random social networks that has a standard API for passing a title and a URL (as most networks already do).
There are few extra things I find useful but they are not implemented yet. Limiting the number of characters for a popup (to avoid annoying popups on every character), fine tuning of the area limits (to avoid sharing menu items, for example) and several more, so – as usual – pull requests are welcome.