RuneLite is free, open-source and super fast. You can download the RuneLite launcher below or contribute to the Runelite project on GitHub.
Download for all platforms
Integrates with Discord's Rich Presence to display what you're doing in the game and allows to form in-game parties

Renders game using your GPU, which provides better FPS, increased draw distance, enhanced scaling and anti-aliasing.
Shows kill count and drops with prices from monsters you kill.

Shows boost timers, enemy HP, and other useful overlays.
A Custom Cursor plugin has been added which, when enabled, allows you to change your cursor when hovering the client to one of a number of iconic RuneScape cursors, including the RS3 gold and silver cursors, a trout, and the iconic dragon scimitar. Thanks to @Kruithne and @Trevor159 for making this happen!

Have you ever confused your herbs, seeds, or tree saplings? We've added an Item Identification plugin to help combat that. When enabled, it will overlay the name (or abbreviated name) on the item when in most non-bank interfaces. Thanks to @Hydrox6 for adding this feature.

The Clue Scroll plugin has had support added for Falo the Bard clues, thanks to @Twiglet1022.

There are also several smaller improvements and bug fixes, including:
Enjoy!
- Jordan
Adam:
interface styles: invalidate healthbar cache on shutdown
travis: update dist to xenial
travis: switch to openjdk8
client: add custom cursor plugin
world hopper: disable Hop-to pvp worlds from regular worlds
Alexsuperfly:
slayer: add 'south of' to task regex
slayer: add test including 'south of'
Beau:
Optionally prevent virtual levels from effecting total level
Crow:
Fix bronze dart requirement in skillcalculator
Hydrox6:
clue plugin: add widget scroll feature
ammo: fix the infobox not getting removed
client: add item identification plugin
TheStonedTurtle:
chat history: fix pm cycling deque max size
chat history: clear friend deque when clearing pm history
Tomas Slusny:
Fix Mutated Zygomite fungicide weaknes threshold
Use proxy methods for settings cursor via ClientUI
Twiglet1022:
worldmap: add Battlefront teleport
clue scroll plugin: add Falo the Bard clues
beaumitch:
npcindicators: Add option to highlight NPC name in right click menu
langhillie:
daily task plugin: add Thirus's dynamite
xDemoN:
idlenotifier: add support pottery crafting
zaydsalah:
Add Herbiboar support to the Loottracker