I've used Audacity previously, and IIRC, I was able to use FX while tracks play. (???)
My biggest issue with Audacity was not being able to overcome latency issues with recording. Just couldn't get it to work.

At that time I was using my Zoom R-8 digital recorder as a capture device then loading the wav's into Audacity for editing and mixing.
Have hardly touched Audacity since switching to Reaper.

FWIW, I just had a look and Audacity has had a significant overhaul/update and changed their I/F as well as improved how plug-ins work.