Conference management system
frab is a web-based conference planning and management system. It helps to collect submissions, to manage talks and speakers and to create a schedule.
ruby
Overview - Redmine
Redmine is a flexible project management web application. Written using the Ruby on Rails framework, it is cross-platform and cross-database.
Edabit
Learn to code with interactive challenges. It's the fastest, easiest, most addictive way to learn.
RIP Tutorial (Stack Overflow Documentation)
Documentation on languages such as C#, Entity Framework, SQL, and a lot of more!