It's interesting working with this kind of limited instruction set.

I made a thing that fills the memory with the sequence of numbers from LEN to 1 and outputs it.

          BRA START
  DEST    DAT 60 // Where to start writing
  LEN     DAT 40 // Size of the sequence
  UNIT    DAT 1
  START   LDA DEST
          ADD STOREI
          STA STOREI
  LOOP    LDA LEN
  STOREI  STA 0 // Self modifying code be here
          OUT
          SUB UNIT
          BRZ END // Halt after writing last number
          STA LEN
          LDA STOREI
          ADD UNIT
          STA STOREI
          BRA LOOP
  END     HLT

This is surprisingly fun!