Chalk produce, and thus widely used in the developing world, calcium-based chalk can be made where the crumbling particles are larger and thus produce less dust, and is marketed as "dustless chalk". Colored chalks, pastel chalks, and sidewalk chalk (shaped into larger sticks and often colored), used to draw on sidewalks, streets, and driveways, are primarily made of gypsum. Chalk is a source of quicklime by thermal decomposition, or slaked lime following quenching of quicklime with water. In southeast England, deneholes are a notable example of ancient chalk pits. Such bell pits may also mark the sites of ancient flint mines,
Blackboard Inc. Engage. In March 2012, Blackboard acquired Moodlerooms Inc. and NetSpot of Adelaide, Australia, which then became the basis of Blackboard's Open Source Services division. From January 2014 to April 2015, Blackboard acquired nine companies, including: MyEdu, an Austin-based online education company; Perceptis, a provider of help desk and administrative services; CardSmith, a company that offered cards for student ID and on-campus payments; Requestec, a provider of technology for VoIP, video conferencing and instant messaging; and Schoolwires, a company that specialized in building school websites. In August 2015, Blackboard acquired Colombia-based Nivel7, possibly the largest Moodle services provider in Latin America.