VEMS is a commercial engine management system. VEMS is unlike most other EMS's in that it used to be public domain and then a form of open source. VEMS is a commercial engine management system. VEMS is unlike most other EMS's in that it used to be public domain and then a form of open source. The original version of VEMS was called MegaSquirtAVR and was a re-write of the popular but inadequate (at the time) MegaSquirt system. VEMS can be purchased as a pre-made board or a complete system with several options in between. Most of the design is built with SMD components to keep size down and reliability up. VEMS uses the AVR Atmega128 which is significantly more powerful than the original MS1 CPU.