One of the best things about the GameCube is the fact that it offers a digital port which allows you to get a really good image out of the console, but sadly this isn't the case for all models of the machine.
While the original DOL-001 variant has Digital AV Out, the revised DOL-101 lacks it, which means you can't get the best image out of the machine via HDMI adapters or component cables.
Modder citrus3000psi tackled this problem a few years back with his commercially available Gamecube DOL 101 Digital Port Upgrade Kit, but this hasn't been in production for some time now.
Thankfully, citrus3000psi has now released the relevant files to GitHub, which means anyone can fashion the parts required to make the kit.
You'll still need to obtain the other components, so it's not a 'free' mod as such, but this is great news for those of you who've always wanted to upgrade your GameCube but haven't been able to source one of the kits.