Use Drafts to quickly note down tasks and notes. And if you do a task quickly, mark it done. Do you want to clean up the draft and receive any pending tasks per mail? Invoke QuickNotes action.
QuickNotes is a Drafts action which:
parses current draft looking for tasks and notes
sends each pending task individually per mail, e.g., to allow Outlook users to flag them as a task
archives current draft by appending it into the monthly QuickNotes archive draft
I do not have any experience with OmniFocus, sorry.
However, looking quickly at the Integration Guide Using OmniFocus with Drafts, it looks like you can send a mail to OmniFocus, so just configure the correct email address after installing and running QuickNotes.
Or, perhaps, there seem to be already many actions cooperating with OmniFocus, e.g., Markdown Tasks to OmniFocus