Software that circumvents rate-limiting. Axel (still available in Archlinux repos at least) can be told to use some number of connections, it'll figure out the size of what you want to download, divide it into the number of connections you want, and start the connections in parallel, each getting a different chunk. Works when the rate limiting is per connection.

Other rate-limiting strategies like slowing down a connection over time would need other "acceleration" strategies like restarting the connection when it slows down, continuing from where the previous left off.

Another possible option that isn't about circumventing rate-limiting but just speeding up downloads can be to download different chunks from different mirrors, to spread the uplink burden. Axel can be provided multiple URLs for this.