>Lets Play Math is a (mostly) free website for mathematics. Tons of great K -12 math resources! In particular there is a math writing prompt site which offers great ideas to help get started writing about mathematics.
>Weird Converter The site is simple: it is like a currency converter, but for completely unrelated items. Play around, see what kind of weird conversions you can make. Or try sensibleunits.com and convert boring objects into real objects.