I don't know if someone's made better tools, but I just pushed onto github a basic AT assembler I hacked together somewhere around 1 - 2 weeks ago:
https://github.com/BurstProject/ATAssembler/blob/master/src/scala/ATAssembler.scalaNo docs on it, but for an example I was using this AT for to stress test API call abuse on testnet is:
start:
FUN @createtime get_Creation_Timestamp
SET @currenttime $createtime
toploop:
FUN A_to_Tx_after_Timestamp $currenttime
FUN @aiszero check_A_Is_Zero
BZR $aiszero :start
FUN @currenttime get_Timestamp_for_Tx_in_A
JMP :toploop
That is very good, i am coding straight in machine code, but this tool might be very useful for newcomers. Nice work!