Vestemi. It has the modest aim of cutting the UK's entire carbon footprint by 10% (and/or Europe's by 8%) at low cost. The aim is halving space heating costs, especially for homes, in a simple and fiddle-free way! (Trueman: "It's amazing how much can be accomplished if no one cares who gets the credit.")
With a little effort, and no hardship, my family and home/office seems to have managed to cut down to ~33% of average 2007 UK household electricity and gas consumption and indeed as of 2010 we're roughly net "zero carbon" for them. I've had a lot of fun getting to understand a little better our energy consumption and how it might evolve in the future, with us even possibly going 'carbon-negative' and becoming net exporters of energy...
I run ExNet Ltd, a company focussed on networked, distributed and parallel software based in the south-west of London (16 Willingham Way, Kingston-upon-Thames).
See my gallery of multimedia (mainly JPEGs) for Web sites; historically one of the most popular photo/art sites in the UK with several million vistors per year. One interesting aspect was developing and tuning Google's AdSense contextual ads.
I give away some of the code I write in the hope that it will be useful to others and save a few wasted hours here and there... Remember: a month hacking code can often save an hour's reading and thinking!
I find this public-domain list of the first 100,000 primes useful in day-to-day coding so I've put up my local copy.