Which kinds of "one step checkout" softwares are the most effective in current market?
How to install them?
You should choose One Step Checkout extension according to your needs and requirements. For example, if your Magento store is responsive, the checkout should also be responsive.
You can also consider our Single Step Checkout
The effectiveness really depends on your target audience. One step checkout where everything (addresses, billing information, order summary) is placed on one page is extremely popular. It's the one that Amasty suggested in the previous reply, however there are more extensions like that.
I ran a bit of research about the usability of one step checkout process and people have different feedbacks - check this article. Sometimes it makes sense to go with a multi-step process like this one http://www.magentocommerce.com/magento-connect/gpmd-checkout-suite.html/. Magento native checkout is also multi-step, but a bit confusing.
If you are really concerned about conversion on checkout I'd recommend trying two scenarios and run some tests to see what option converts more because what works for one site might not work the same for the other.
Magecom | Magento e-Commerce Development
Here is the extension we can offer you http://ecommerce.aheadworks.com/magento-extensions/one-step-checkout.html
The One Step Checkout module is really popular among our customers and has broad functionality due to multiple improvements.
You can use the following One Step Checkout Extension by Fme which comes with the text box feature to let customers writer a message to the merchants while placing the order.
Checkout our One Step Checkout extension with tons of features and very easy to install. Even we do help with the installation on live chat if you have any trouble. At very affordable Price, we are offering this extension, you will must feel, that it is worth for this Price.
One Step Checkout : https://www.magecomp.com/magento-one-step-checkout.html
Almost of online shops are facing to card abandonment problem. One of reasons that cause it is that checkout process is too long.
I am suggesting all of you a Magento One Step Checkout as a best solution helping your site increase conversion rate and sales fast.
Go to: http://www.advancedcheckout.com/one-step-checkout-features.html?utm_source=forum&utm_medium=organic for more information
For Magento 2, this One Step Checkout extension cannot be ignored to get a better and more responsive checkout interface
+ Merge two checkout steps in the Magento default into 1 step only
+ Auto locate customer places and also use Google Suggest to autocomplete customer addresses when typing some letters
+ Auto update information when related things change
+ Add delivery dates and time for customers to select and also allow them to leave delivery comments for their orders
+ Support multiple payment methods
+ Support more options for the checkout page: discount code, gift message and newsletter subscription
You can check out this AJAX-driven Quick One Page Checkout extension for Magento. With it all information needed for checkout can be filled in on the same page without steps and reloads. Guests can easily register directly on checkout. Also you may enable Terms and Conditions that will appear in a popup before placing the order.