Slim AJAX Loading Indicator Library – microbar
microbar is a very small and easy to use JavaScript library for generating a top slim progress bar to indicate the ajax loading status
JavaScript & CSS loading bar
Slim Progress/Loading Bar In Native JavaScript – loadbar
loadbar is a tiny native JavaScript plugin for creating a slim progress & loading bar which can be attached to any container or the whole document.
Medium-style Loading Bar with JavaScript and CSS3 Animations – app-loading
app-loading is a minimalist JavaScript library used to show a Medium.com style app loading bar with smooth CSS3 animations.