No exam is compulsary. There are a number of exams - CAT, XAT, MAT, NMAT, CMAT, SNAP, MHCET, IIFT, TISSNET, JEMAT, etc. Different college uses different exam to shortlist candidates for the next round. Some colleges use more than one exam also. Hope this helps!

No, CAT or CMAT exam is not compulsory for MBA. There are a host of other MBA entrance exams similar/euivalent to CAT like XAT. Several institutes have their own entrance exams like NMAT for NMIMS, TISS, SNAP for Symbiosis, IIFT, CET for Maharashtra institutes, MICA, etc. XAT scores are accepted in all B schools almost now so you have plenty of options. There are couple of non-famous institutes also that offer MBA courses without any entrance score based on your BBA performance only.