A number of new Citizen Science projects and Smart City initiatives have the common challenge of providing a smartphone with functional- ity to consume data and / or produce data. For many of these projects the data contains location information, and a common use case is to vi- sualize the data on a map. With these commonalities, it should not be necessary to start from scratch each time a new smartphone application is developed. The following research question is addressed in this thesis: How can anyone with an idea for an application within the field of Smart City and Citizen Science realize it in a time and cost effective manner? The first part of the thesis is addressing the motivation and problem definition for rapid development of Smart City and Citizen Science applications. Based on this a set of different requirements in five different categories is presented. These requirements area applied for the evaluation of existing mobile application development tools in the groups of generic and specialized frameworks. The main part of the thesis is presenting CITAPPLAB with vision, design, implementation and validation on a practical example. The toolkit, CITAPPLAB, provides a common simplified interface to work with different data sources, such as CKAN, NGSI, SPARQL, WFS and REST. With a common interface, it will be easier and faster to use data from different sources in the application. The final part of the thesis is evaluating CITAPPLAB according to the initial requirements as a basis for the conclusion and further work. Further work includes in particular the usage of CITAPPLAB in the context of hackathons for the rapid development of Smart City and Citizen Science apps, based on the usage and extensions of the current CITAPPLAB open source toolkit.