Gradelink - Gradelink is a one-stop-shop system for K-12 schools. You can see grades, attendance, tuition, admissions and communication in one place.
Typora - A minimal Markdown reading & writing app.
Infinite Campus - Access your (or your child's) schedule, grades, assignments and attendance data using the...
Dillinger - joemccann has 95 repositories available. Follow their code on GitHub.
Administrator's Plus - Cloud based student information management software
StackEdit - Full-featured, open-source Markdown editor based on PageDown, the Markdown library used by Stack Overflow and the other Stack Exchange sites.