Cyclobenzaprine (brand name Flexeril) is not the least bit recreational and in higher then recommended doses is also Cardiotoxic. Basically it's a Tricyclic that instead of being used for depression is used as a muscle relaxant probably because it bombed out as a anti-depressant. It is structurally similar to Amitriptyline and acts much like Nortriptyline due to it's Norepinephrine reuptake inhibitor effects and also it's strong anti-cholinergic activity.
Some people find it to work well at potentiating opiates but i have Flexeril so i never use it for that purpose. On it's own it certainly has no recreational effects at all and is pretty useless as a muscle relaxant as well. Personally id much rather Valium or even Orphenadrine as a muscle relaxant over Cyclobenzaprine.