Precision farming and in-field phenotyping benefit from developments in robotics. However, the technological advances are usually dedicated to large scale facilities, either monoculture farms or research facilities. We introduce the LettuceThink robotic platform as a versatile tool to ease the work on market farms. The design and software are modular and open source so that it can be built with standard parts and modified to fit specific needs. We demonstrate its use with two applications: precise mechanical weeding and 3D reconstruction of plants.