all trime great ultra light weight browsers

• K-Meleon

K-Meleon is a browser powered by Gecko engine, that aims to be very fast, widely customizable and extremely lightweight. The software is free and open source as well as simple and straight forward. Don't be deceived by the simplicity, the browser has a powerhouse of options that makes it lean and mean. The preferences panel has daunting number of options (presumably the largest among any browser) to customize the browser that can even shy the biggest names in the market. 

K-Meleon also supports a decent number of extensions to increase the flexibility of the browser. K-Meleon implements mouse gestures that makes your browsing experience more comfortable. Managing and organising bookmarks is very easy and they can be imported as well as organized well, in folders. The privacy options lets the user to be safe and clear any sensitive data that may be stored and K-Meleon lets you to manage cookies, login data, history, cache, referrers, user agent string and prefetching link addresses as well as implements encrypted transmission and storage. 

There is also an endless list of search engines by default in K-meleon and which can be added at will and also has a built-in RSS reader. You can filter the contents of webpages through CSS rules for ad-blocking.  K-Meleon utilizes its cache very well and was the fastest to load webpages for consecutive times. 

The browser has been a pleasure to use and is the best bet on old hardware because of it being extremely light. Though the abundance of options in K-Meleon would interest any advanced user to lean against it, the browser has been made to rot without any significant updates for quite some time.

• QtWeb 

QtWeb Internet Browser is an open source project based on Nokia's Qt framework and Apple's WebKit rendering engine (the same as being used in Apple Safari and Google Chrome). It's the best portable browser in my tests and consists of just a single portable exe file.The browser has the fastest startup time among all I've tested.

The user interface is minimal which can be changed by using application styles icon. The browser is also customizable with options to show/hide buttons, toolbars, relocate navigation bar and bookmarks, even undock them to desktop. The browser supports FTP browsing and downloading as well as have a built-in torrent client. The browser also supports mouse gestures, keyboard and mouse shortcuts (can be studied from new tab page) and open/play audio, video content in external applications.

I love QTWeb, especially because of its privacy and security. The browser being highly portable is a single button click away for turning on private browsing. It even runs in a limited Windows environment or directly from USB. There are options to 1. reset the browser(clear history, back to defaults etc) and 2. full reset(back to clean state). There is also an inbuilt adblocker which can be customized to block those nasty ads.

There are also additional useful options like Auto-Fill support, web inspector to inspect html elements and reduce load times, virtual keyboard support etc. Though, there are been occasional rise in memory usage, the browser is still extremely lightweight and is a small 6MB download. 

• Midori

Midori (Japanese for green) is a web browser that aims to be lightweight and fast. It uses the WebKit rendering engine and the GTK+ 2 interface. Midori is part of the Xfce desktop environment's Goodies component.It is the default browser in elementary OS and the BodhiLinux distribution as well as Trisquel Mini.

• Arora

Arora is a lightweight cross-platform web browser. It runs on Linux, embedded Linux, FreeBSD, Mac OS X, Windows, Haiku, and any other platforms supported by the Qt toolkit.Arora uses the QtWebKit port of the fully standards-compliant WebKit layout engine. It features fast rendering, powerful JavaScript engine and supports Netscape plugins.

• Avant

Avant Browser is an ultra-fast web browser. Its user-friendly interface brings a new level of clarity and efficiency to your browsing experience, and frequent upgrades have steadily improved its reliability. Avant Browser is the lowest memory usage web browser on Windows platform (website claim).

• QupZilla

QupZilla is a lightweight multiplatform web browser written in Qt Framework (same as QtWeb browser) and using its web rendering core QtWebKit. It features SpeedDial extension and integrated AdBlocker and uses native widgets style with a unified library for bookmarks, history, rss and the like.

• Columbus Browser

Columbus is a smart and powerful web-browser with many useful built-in features. It has the ability to search for a particular file you want to download, directly on all popular torrent sites and offers a quick, reliable access to Web content, ease-up your downloading habits or help you with your online work. 

• GreenBrowser

GreenBrowser is based upon the Trident rendering engine used in Internet Explorer. GreenBrowser is a full-featured powerful and flexible browser, highly-customizable but compact in size and low in memory requirements.GreenBrowser is similar to Maxthon and closely related to the MyIE browser.

• TheWorld Browser

TheWorld Browser is a tiny, fast, secure and powerful web browser created by Phoenix Studio. It a multi-tab and multi-window web browser. It is completely free and there is no function limitation. It has no bundled software, so it can be uninstalled totally.  

• Slimbrowser

SlimBrowser is a free web browser for Windows that is blazing fast, most secure and fully loaded with powerful features. It starts up quickly and opens web pages right in front of you with minimum delay. It is designed to let you browse the Internet safely by guarding your personal information and protecting your privacy.