STRAP is described as '(STRuctural Analysis Programs) is a Windows based suite of finite element static and dynamic analysis programs for buildings, bridges and other structures'. There are more than 25 alternatives to STRAP for Windows, Linux and Mac. The best alternative is midas Gen. It's not free, so if you're looking for a free alternative, you could try SkyCiv Structural 3D. Other great apps like STRAP are midas Civil (Paid), RISA-3D (Paid), RISA-2D (Paid) and Etabs (Paid).
SkyCiv Structural 3D is a powerful structural analysis and design software on the cloud. Nothing to install or download and users can subscribe on a month-to-month basis so there's no life long commitment. It's also free to get started.
For nearly 30 years, ETABS has been recognized as the industry standard for Building Analysis and Design Software. Today, continuing in the same tradition, ETABS has evolved into a completely integrated building analysis and design environment.