http://digitalistechnology.co.uk/ - makers of the Digitalis CPD app, which is designed "by GPs for GPs" to help you find and record online learning. We're listed on their website!
http://www.scionpublishing.com - Publishers of Professional Development for Appraisal and Revalidation - The Dr Hairy Workbook, and they publish a lot of other interesting stuff too. They've also been unfailingly friendly and helpful to us in developing the Dr Hairy project.
http://www.gp-update.co.uk/ - Another unfailingly friendly and helpful organisation. They're the ones who put us in touch with Scion Publishing; and like us, they try to present their training in a way which is down-to-earth, humorous and user-friendly.
http://www.kdenlive.org/ - Open-source video-editing software. Much less buggy than it used to be, and very intuitive to use. Can process video in a whole range of different formats, and outputs to a whole range of different formats too, although this is a little bit complicated to set up.
http://www.blender.org - Primarily this is open-source 3D animation software, but it can also be used as a video editor and compositor. Complicated but immensely powerful. All the green screen effects in the Dr Hairy videos are done with Blender.
http://audacity.sourceforge.net/ - Open-source audio recording, editing and processing software.
http://www.gimp.org/ - Open-source image processing software - a fully-featured alternative to Photoshop or Fireworks. All the Dr Hairy titles and stills are done using the Gimp.
https://www.freesound.org/ - A huge online library of free sound-effects. This is a brilliant site! A dripping tap, a ticking clock, a telephone ring, a buzzer, a beeper, the sound of background conversation at a party, the sound of somebody's gooly being sliced off by accident... you can get it all from Freesound.
http://www.concrete5.org/ - "A simple but powerful content management system". The website you're looking at now is made in Concrete5. Open-source, although we've bought a number of (very reasonably-priced) add-ons to enhance it (such as the e-commerce add-on). As CMS systems go, this one is really easy to use.
https://moodle.org/ - The "open-source learning platform". Dr Hairy's Online Training is built using Moodle. A bit like Blender, this is complicated to learn but really powerful once you get the hang of it.
https://www.openoffice.org/ - The open-source alternative to Microsoft Office (although there's another, closely-related alternative called LibreOffice). All the layout for our self-published books was done using OpenOffice.
http://www.scribus.net - Open-source page-layout software, an alternative to things like InDesign and QuarkXpress. Another one which is a bit complicated to get the hang of, but very powerful. The covers of Dr Hairy's Professional Development Pack and the Dr Hairy in... DVD were designed using Scribus.
http://www.lulu.com - The self-publishing, print-on-demand website we have used to produce our books, Dr Hairy's Guide to the GP Curriculum and Dr Hairy's Research Summaries. There are lots of self-publishing organisations around now, but Lulu was the first.