Full Lightning features list

Engine Optimization

events preprocessing (events system works tens times faster)
frequently used data is collected in a special pack, that is loaded at the OpenCart start (negate the need of most repetitive queries that are executed on every page creation)
MySQL queries slower than 0.05 seconds are cached with intelligent deletion of corresponding cache records on data change
optimization and grouping MySQL queries (drastically reduce the number of database queries and speed up many slow queries)
fixed vQMod performance problem in OpenCart 3

caching of critical pages (homepage, categories, manufacturers and sitemap) + product pages
an option to cache all pages except a certain type (route)
actual mini-basket is mounted into cached page
actual wishlist and compare numbers are mounted into cached page
pages for logged-in customers are created from regular cached pages
currency conversion on the text of the cached page that allows you to keep only one set of the cache with main currency
caching AJAX requests from pages that are subject to caching
background pregeneration of cache pages to a distance of 2 clicks from the starting or current page
any page visit starts a background pregeneration of pages to which there are links from this page, so visitor will get the next page from cache
optional separate cache pages for mobile and tablet devices
automatic deletion of appropriate cache pages on products modifying or deleting (monitoring database queries and date_modified change by external scripts)
ignoring URL parameters with information from the ads traffic (this way they get a page from the cache, not generated new)

automatic setting of the optimal level of GZIP compression of pages (setting in admin is ignored)
proper static resources headers, caching and compression is written in subfolders .htaccess files (its better to remove such an instructions from the root .htaccess file, if you have added them)
JS and CSS resources grouping and minification
correct transfer of all scripts to the page footer
external resources from other servers are included into group file and minified (at Aggressive optimization levels)
2 levels of JS script defer (at Aggressive optimization levels)
automatic critical CSS creation - it is used before all CSS is loaded
background image optimization via CRON task which runs on most hostings and does not require the exec() function and utils installation
if CRON task doesn't work, Lightning can optimize images with external utilities (like jpegoptim and optipng)

checksums of all pages is tracked to serve actual Last-Modified headers, that dramatically speeds up search engines indexing
fixes canonical, prev and next links in the categories of level 2 and deeper, which led to duplicate category pages
number of products per page limit protection (limited to 100). Requests with huge limits are used to take the shop down
products links unification into shop.com/product-url form (with path of the deepest category displayed in breadcrumbs). With this search engines indexing becomes much faster and number of pages to be cached reduces dramatically
automatic index.php?route=common/home homepage links fix
special instructions are added to robots.txt to prohibit search engines indexing of unnecessary pages (with changed sorting, number of products per page, etc.) - speeds up indexing and reduces the load from search engines

the Clear Cache button (clears Lightning caches, system cache, and the cache of the JOURNAL theme)
statistics display - cached pages, AJAX and database requests, optimized images, the average TTFB (time of page generation) with Lightning and without it
display real-time TTFB of the last served page, that allows to evaluate the "pulse" and speed of the shop
a visual real time display of all visited pages indicating the IP, agent and response time
free space on your server display (helps to react before situation become critical)
widget is only shown to users with the right to modify setting/setting - thus you can hide the widget from the managers
double click on the Lightning version number toggles the widget into "customer mode", hides everything except the buttons to Enable/Disable and Clear Cache

MySQL queries slower 2 seconds
MySQL queries with result more than 5000 rows or more than 1 Mb capacity
fatal errors that occur during operation of the store (much clearer and more informative than OpenCart log)
missing JS/CSS files
recommendation to upgrade to PHP7, if the server has lower version
the recommendation to change robots.txt if it is not possible to do automatically
instructions how to translate the store into full HTTPS, if you have not done this or done incorrectly
instructions for configuring the CRON tasks for pages pregeneration and optimizing images

the ability to display multilingual cookies notices (many other implementations do not work correctly with pages caching)
when you add a URL parameter li_sql=1 the execution time of the controllers and queries is displayed
when you add a URL parameter li_module=1 modules information is displayed (useful when it is necessary to define the module name to load via AJAX)
when you open index.php?li_op=lg shows handy logs viewer with realtime update
when you open index.php?li_op=cn the results of connection to Lightning server and other servers is displayed (in order to understand whether the hosting allows external connections at all)