A few free bots are
- PowerBot (some scripts are free)
www.powerbot.org, easy to use
- Simba (most scripts are free)
www.villavu.com, a little harder to use
- RiD's free bots (powerminer is free)
www.robotzindisguise.com, takes control of mouse
All 3 are pretty well known and all 3 are good in my opinion, but for simba and powerbot, you need to look for the scripts with the most positive feedback
RiD also has a free construction bot, and each user is given a free 6 credit trial (usable for 4-6 hours of botting depending on the bot) every month (assuming they have 0 credits by the time the next month starts, meaning if you have 1 credit left, and the next month starts, you don't get another trial until you use all of your credits and the next month comes.
Also, normally it does use your computer's mouse, however it only takes ~15-20 minutes the first time to set up a 100% free, genuine, and legal VM running the customized version of Windows XP designed specifically for use with botting RiD in VirtualBox VMs. They have a free, easy to follow guide in their Knowledgebase Extras section.
Also, botting is about to get extremely dangerous for most bot sites once Botany Bay and the Anti-Botting system is released. RiD will not be affected by this system however, neither by graphics updates (less than a day or two to update), nor by bans. There actually has not been a single ban whatsoever from RiD in over a year, even out of the suicide botters, and that will stay the same through this anti-botting update. RiD is the kind of software that has been used by users who have max total levels, Player Mods (I've personally helped multiple P Mods set up RiD for use on their P Mod accounts), uber-rich players (I'm talking 20bil+), and by regular players who care about the safety of their account and would be devastated if their main was banned. Before Botany Bay getting banned with a detectable bot was vastly related to luck of not getting caught; after Botany Bay it will no longer be luck, as every single account in the game will be monitored simultaneously using this new system. The bots you use will actually have to pass as human to stay under the radar, and RiD is actually exactly that. It's been around since 2007, and was brought to its current quality on August 10th, 2008. From August 2008 until late summer of 2011 there was only 37 bans (mostly temps), and out of every single one of those users, they were repeatedly and consistently breaking the site's Botting Guidelines. There has yet to be any bans by any users following Guidelines, and the statistical rate of being banned breaking the Guidelines is realistically less than 0.01%.
I myself have used their bots for 3350 hours (2632.5 premium and 716.9 free), earning me 13 99s (I'm less than 2mil exp from my 14th) on my main, plus 99 fletching on my mule. My main, with these bots, has over 200 million exp. My botting goal with RiD (and this is realistic I might add) is to get max cape + 2496 total level + 1 billion total exp. This means I will have to get max total level and then get 200 mill exp in 3 separate skills. Thieving, and Firemaking are two of these skills I plan to go for 200m, and RiD has already had multiple users reach 200mil exp in one or both of these skills with these bots, and still no bans. I've actually quested on one of the accounts that had 200mil thieving, and I about shit my pants when I saw it.
I know you said that you don't want to pay, and there are many free options out there, however I'm more worried about your RS account safety from macro bans after this Botany Bay update than your wallet. Most if not all scripters you find around sites like Powerbot, Epicbot, etc are in high school or are just entering Uni, and thus lack certain skills and educations in regards to programming. RiD, the Admin and lone Programmer, has his Bachelor's degree in Computer Science and Mathematics. He was even interviewed by Jagex around 2005 or so for a position on their staff because of his programming and graphics knowledge. You can be sure that you're using a very professional product that won't have shortcuts taken to save time at the expense of his user's safety. Curious as to how the anti-bot update will effect RiD and the rest of the botting community? Wait a few weeks, and then once it's launched check around the different botting sites, RiD included, and see how many people have been banned. Honestly, pick whatever you want. Choosing the bot that is most suited to your needs is your decision and you know what you want out of a bot site. It's really all up to you