OmniSharp server (HTTP, STDIO) based on Roslyn workspaces
Core server and tier 1 (built-in) plugins
Open Source Java Application Server Derived from GlassFish
Imixs Workflow - the open source business process management
Open Source Continuous Integration & Deployment Server
Poll JMX attributes from Java based applications with Nagios
Free report server for creating data-driven apps
Full featured open source BRM/BPM/CMS stack