Each time I've seen something about GNU parallel pop up I've been tempted to post, but I've never made an account until now.
I wrote a very different style of command parallelizer that I named lateral. It doesn't require constructing elaborate commandlines that define all of your work at once. You start a server, and separate invocations of 'lateral run' add your commands to a queue to run on the server, including their filedescriptors. It makes for easier parallelization of complex arguments.
Take a look if this sort of thing interests you, as I haven't seen anyone write one like this before. Its primary difference is the ease with which each separate command can output to its own log, and the lack of need to play games with shell quoting and positional arguments.
Check it out: https://github.com/akramer/lateral