1. meanwhile
  2. Zarf incidentally
  3. by the way
  4. Zarf by the by
  5. among other things
  6. in the meantime
  7. Zarf by the bye
if nothing intervenes
On another note,
Meantime, Zarf
Speaking of which, ... Zarf
On an unrelated topic, ... Zarf
One more thing, ...
in the mean time