Simple Page Title is a module exclusively designed to provide Search Engine friendly title tags for SEO purposes. Titles can be applied to any kind of page whether it is a node, a user, a view, a "hard coded" page created in a custom module or any other kind of page.
The way this module works is that the text for the title tag is assigned to a URL path. This can be a standard drupal URL (e.g. node/1, user/3) or a friendly URL generated from a module, path or pathauto (e.g. news/todays-latest-news). Simple Page Title is different from the standard Page Title module in that by assigning the title to the url path it can handle assigning titles to things like views and panels where the standard Page Title module can have trouble with these things.
Conversely, Simple Page Title is only a basic module and does not have most of the functionality of Page Title, such as Token Integration. It is designed purely with SEO use in mind and has an easy to use interface for SEO professionals who may work on websites (in addition to being user friendly for regular Drupal users).
Simple Page Title + Page Title?
For users who wish to use Simple Page Title and Page Title together the two modules are compatible. There is an admin screen which will decide the weighting of the module (to determine which module runs first in the event that a page will have titles set by both modules).
There is an open issue on the issues page where I encourage discussion about new features for the module and what else people would like to see happen with Simple Page Title. Then, time willing, some of these things will actually happen!