Team communication is essential for the development of modern software systems. For distributed software development teams, such as those found in many open source projects, this communication usually takes place using electronic tools. Among these, modern chat platforms such as Gitter are becoming the de facto choice for many software projects due to their advanced features geared towards software development and effective team communication. Gitter channels contain numerous messages exchanged by developers regarding the state of the project, issues and features of the system, team logistics, etc. These messages can contain important information to researchers studying open source software systems, developers new to a particular project and trying to get familiar with the software, etc. Therefore, uncovering what developers are communicating about through Gitter is an essential first step towards successfully understanding and leveraging this information. We present a new dataset, called GitterCom, which is meant to enable research in this direction and represents the largest manually labeled and curated dataset of Gitter developer messages. The dataset is comprised of 10,000 Gitter messages collected from 10 Gitter communities associated with the development of open source software systems. Each message was manually annotated and verified by two of the authors, capturing the purpose of the communication expressed by the message. While the dataset has not yet been used in any publication, we discuss how it can enable interesting research opportunities in the field.