If you just need it for Windows, you should consider HTML Applications (HTA), it's been part of Internet Explorer since IE 5 (10+ years).
No server required, full HTML formatting, full access to local resources (even COM / USB ports), awesome. Also, easy to debug with Visual Studio, just bind to MSHTA.exe
You can enable HTML 5 in HTA's with the following meta tag:
<!-- enable html5 features -->
<meta http-equiv="X-UA-Compatible" content="IE=edge"></meta>