Figure 1: Varv Examples: (a) A todo list web application that is inherently extensible. Here, a basic todo list is extended with the ability to complete and delete todos by adding two new concept defnitions and new modifed template defnitions. (b) A board game toolkit that defnes abstractions for board game logic. The games "Checkers" and "Othello" were implemented with the toolkit and then merged into a new "Checkers-O-Thello" game with the addition of a short concept defnition. As Varv applications are represented as data structures, higher-level tooling can be developed including a block-based editor (right), an inspector to go from an element in the view to the corresponding template or data (context menu to the left), and a data inspector for live editing application state (middle).

We present Codestrate Packages, a package-based system to create extensible software within Codestrates. Codestrate Packages turns content creation from an applicationcentric model into a document-centric model. Codestrate Packages no longer restrict users to the feature set of the application. Instead packages allow users to add new features to their documents while already working on them. They can match the features to their current task at hand. Supporting the reprogrammable nature of Codestrates, new features can also be implemented by users themselves and shared with other people without having to leave the document. We illustrate the application of Codestrate Packages in an example scenario and present its technical concepts. We plan to conduct multiple user studies to investigate the benefits and barriers of Codestrate Packages' documentcentric approach.

The popularity of computational notebooks heralds a return of software as computational media rather than turn-key applications. We believe this software model has potential beyond supporting just the computationally literate. We studied a biomolecular nano-design lab that works on a current frontier of science -RNA origami -whose researchers depend on computational tools to do their work, yet are not trained as programmers. Using a participatory design process, we developed a computational labbook to concretise what computational media could look like, using the principles of computability, malleability, shareability, and distributability suggested by previous work. We used this prototype to co-reflect with the nanoscientists about how it could transform their practice. We report on the computational culture specific to this research area; the scientists' struggles managing their computational environments; and their subsequent disempowerment yet dependence. Lastly, we discuss the generative potential and limitations of the four design principles for the future of computational media.

Programming assignments in computer science courses are often processed in pairs or groups of students. While working together, students face several shortcomings in today's software: The lack of real-time collaboration capabilities, the setup time of the development environment, and the use of different devices or operating systems can hamper students when working together on assignments. Text processing platforms like Google Docs solve these problems for the writing process of prose text, and computational notebooks like Google Colaboratory for data analysis tasks. However, none of these platforms allows users to implement interactive applications. We deployed a web-based literate programming system for three months during an introductory course on application development to explore how collaborative programming practices unfold and how the structure of computational notebooks affect the development. During the course, pairs of students solved weekly programming assignments. We analyzed data from weekly questionnaires, three focus groups with students and teaching assistants, and keystroke-level log data to facilitate the understanding of the subtleties of collaborative programming with computational notebooks. Findings reveal that there are distinct collaboration patterns; the preferred collaboration pattern varied between pairs and even varied within pairs over the course of three months. Recognizing these distinct collaboration patterns can help to design future computational notebooks for collaborative programming assignments.

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