ATS looks interesting. It continues to boggle my mind that Ada/SPARK isn't given more attention in conversations like this. It seems to do everything Rust promises while being simpler (SPARK anyway) and more powerful, and with 40 years of history and experience behind it.
Ada doesn't use a garbage collector, so it appears that understanding isn't right. I think it had one as part of the standard in the 80s, but maybe such problems made it go away.