One may write Torah insights on Chol Hamoed.
Mishna Berura explains - since a person is supposed to study Torah at every moment as much as possible , & to write it down , if he waits until after Yom Tov he will lose time from studying more thus it is considered a Dovor haovaid.
Now may be a good time for a gem of Torah study.
www.GemsofTorah.com