It's free extension for Opencart, it will add checkout with just one step.
The module is installed by OCMODE installer and do not replace any native files.

IT'S TESTED ON 2.3.0.2 version ONLY, but it must compatible and with others versions of OPENCART 2

UPDATING 12.12.2017
Added thumbnails in list of products. And removed some links in the login modal window

UPDATING 15.05.2017
added ajax payments and redirect to the payment system if order framed properly (tested just with "PAYPAL Express" and "cash on delivery" methods), popup ajax login form, russian and ukrainian languages.
Some changes added by ex4 ( his version of the extension you can find in the comments below) :
Modified install.xml to change link to checkout also in cart view and header.
* Added support to add coupons or use reward points from checkout page
* Added support for totals -modules.
* When changing shipping method from checkout page it updates total price. Tested with pick from shop and flatrate shipping (the ones I use).

If you found any errors please write about it in the comments


DEMO
{DEMO ( Buy any of products and go to checkout )}

If you have any interesting proposals, for work write to my email: andreyy.derevjanko@gmail.com

Russian description of this extesinon you can find on my website: {Russian desciption}

You can learn more about me on my website: {Andrey Derevjanko website}
GitHub repo - https://github.com/kudesnic/one_page_checkout