Have you already done a 23andMe analysis? If so, you can check out https://promethease.com/. It's exactly what you're looking for as they have constant updates that make it worth your while to rescan every year or so.
Promethease is awesome. I uploaded my 23andMe data to it and got back the kind of data I'd been hoping for in the first place.
Fair warning: the UI is very geeky. I think any HN reader should be able to find their way around without trouble, but I wouldn't recommend it to my non-technical friends or family.
23&Me will let you download a text file with the ACGT data, but only for the SNPs that it has. 23&Me does not sequence your full genome, so the SNPs available are a small subset of your DNA.
Prometheus is not open-source (I think), but all it does is read various files with DNA data (like the 23&me export), and match it up with the information in SNPedia (a Wikipedia-like open repository of what we know about certain SNPs), and then exports it to a pretty HTML/JS web report for you that you can download and save.
Fair warning: the UI is very geeky. I think any HN reader should be able to find their way around without trouble, but I wouldn't recommend it to my non-technical friends or family.