I just started to work a bit more on my side project Template2pdf (http://template2pdf.com/). It is an API to enable developers to produce nice PDFs out of templates that their customers can modify on their own.

It runs on Debian with ruby/rails, java, postgresql and some system tools.

I also do some work on a SAAS to build wireless hotspot systems. I don't own anything of it, but is an interesting field once you hit scalability problems. We use all kinds of technology but the core components would be linux/freebsd, freeradius, postgresql and ruby.