Not sure if you get it in the US the same as in the UK, but I find that even just squash is good with carbonated water, e.g. orange squash. Cheaper than syrups and it tastes good with still water too!
No squash is very different to fresh juice. It's also called cordial but cordial tends to be far "syruppier" and may be slightly different, I'm not sure.
You mix 1 part squash with 6ish parts water (depending on preferred strength) and drink.
Ribena and Robinsons are the squash kings in the UK, just a very easy way to mix up some flavoured water basically.