Eroteme told me about this interesting Wordcount site. The site counts the top 86800 English words and lists them in frequency of use.
I've been thinking for some time that there could be a systematic means to convert the vocabulary in any article (or any written piece) to a simpler level. For example, an article with a word such as 'quotidian' (rated 71479 on Wordcount) would be converted: 'quotidian' would be defined (or replaced with a synonym) using only words from the top 10000 of Wordcount.
Thus 'quotidian' = on-a-daily-basis
('on' rated at 13
'a' rated at 5
'daily' rated at 1350
'basis' rated at 683)
The user could opt for the conversion to use only words from the first 10000 words from Wordcount, or 20000 etc.