Internal tool builders are platforms that let you build custom apps for you and your teammates to use at work. These tools focus on data and functionality, providing flexibility to solve internal business problems. The best internal tool builder depends on the user's needs and skill level, with options ranging from no-code solutions like Glide and Stacker to full-code enterprise-grade platforms like OutSystems. Other notable options include Zapier for automation, Google AppSheet for starting from a spreadsheet, Quickbase for building mini-apps with AI, Microsoft Power Apps for advanced logic without code, Budibase for an open-source solution, Retool for extending with code, and Appsmith for volume-based pricing. Each platform has its strengths and weaknesses, and users should choose the one that best matches their needs and skill level to simplify their work and reduce mistakes.