nailgun
Note: Nailgun is based on original code developed by Marty Lamb. In October, 2017, Marty transferred the repository to Facebook, where it is currently maintained by Buck team. Nailgun will remain available under the Apache license, version 2.0.
Nailgun is a client, protocol, and server for running Java programs from the command line without incurring the JVM startup overhead.
Programs run in the server (which is implemented in Java), and are triggered by the client (written in C), which handles all I/O.
The server and examples are built using maven. From the project directory, "mvn clean install" will do it.
The client is built using make. From the project directory, "make && sudo make install" will do it. To create the windows client you will additionally need to "make ng.exe".
A ruby client is available through the railgun project.
For more information, see the nailgun website.