There are some programs that you make 'scripts' for, and they do what you told them to in the scripts. It's not that simple though. Here they are in order from best to worst (In my personal opinion) -
1. SCAR - Used mainly with an include library called SRL. SRL includes include functions, which make scripter's lives easier. These 'functions' are series of mouse movements, clicks, looking for stuff, etc. When using SRL, SCAR has both reflection (reads the client and uses that info to auto accurately) and color clicking (self-explanatory, uses colors to auto). You don't neccessarily have to make the scripts yourself, although it is fun and rewarding to learn (plenty of tutorials at the SRL-Forums). For more info on SCAR and SRL, go to
www.srl-forums.com. Oh and SCAR is coded in a modified form of pascal.
2. RSBot - I haven't used this much, but it is pretty decent too. However, it uses just reflection, and reflection breaks often and has to be updated. It is coded in Java.
www.rsbot.com for more info.
3. Nexus/iBot - Generally considered to be the most detectable, and (last time I checked, might of changed) it isn't free if you want to be able to use your computer for other things while autoing. I've never used it, and don't plan to. I believe it uses reflection and is coded in Java.
www.rscheata.net for more info.
(Sorry mods if I'm not allowed to post the links, remove them and notify me with a pm please, if they're not allowed)