Use Debian Alternatives to switch between Ruby versions (1.8, 1.9 and JRuby).
Debian Alternatives is a powerful system which allows you to decide which out of many is the implementation of a certain program that you want to use.
It also handles groups of programs which can be selected all together.
How to setup PostGIS in your PostgreSQL database.
How to set up JRuby and adapt a Ruby on Rails application to run on top of it.
When you want to have a central shared git repository to push commits to, there are two common configurations:
1. Everybody uses the same user for commits - easy to set up, but very messy,
2. Create a system user for each committer, create a system group for each project and add users to relevant groups.
The post explains how to set up and manage configuration the second option.
Clojure is a very promising new language that runs on the JVM. It handles concurrency in effective end innovative ways. I've written a mini-guide on how to get started.
GNU screen lets you can have multiple persistent screen sessions, and reload them by name.