As the number of Extended Reach Wells (ERW) with multilaterals and restricted access due to electric submersible pumps (ESP) increases, so does the challenge to enable access and stimulation to these wells to maintain production rates. This paper describes a Slim Access and Stimulation System (SASS) development program launched to develop a game changing technology to give operators the ability to maintain high production rates in unconventional developments. There is available technology today to accurately access extended reach lateral wells, even with restricted access. But the technology is limited to logging only, as the tools and/or control wire are not acid resistant and would limit the pump rate through the coil tubing for pumping acid. The new system would require a tool suite which was acid resistant, enable slim access to the laterals, and have the ability to perform multiple stimulation jobs in one run, with monitoring and control from surface without a wire inside the coiled tubing. The SASS development program gave birth to three separate and revolutionary new technologies: two-way wireless communication and energy harvesting with integrated production logging suite, slim and high-power open hole tractor with a wire bypass to power the tool string, and semi-autonomous lateral access sub, which finds, enters, and confirms the lateral access. The three game changing technologies have application as standalone products, however the real value occurs when they combined as a Slim Access and Stimulation System, run on conventional coiled tubing. The paper will describe working methods and technology incorporated to provide access to restricted extended reach laterals and perform multiple stimulation jobs in a single run. The SASS development program is a testament of how the industry can tackle complex challenges, introducing new technologies across in multiple domains while still adapting to conventional methods. The paper highlights the full system design approach method used to understand and combine features of downhole tools, surface equipment, and operational and handling routines to achieve the overall design goal.