Most safety-critical systems must undergo assurance and certification processes. The associated activities can be complex and labour-intensive, thus practitioners need suitable means to execute them. The activities are further becoming more challenging as a result of the evolution of the systems towards cyber-physical ones, as these systems have new assurance and certification needs. The AMASS project (Architecture-driven, Multi-concern and Seamless Assurance and Certification of Cyber-Physical Systems) tackled these issues by creating and consolidating the de-facto European-wide open tool platform, ecosystem, and self-sustainable community for assurance and certification of cyber-physical systems. The project defined a novel holistic approach for architecture-driven assurance, multi-concern assurance, seamless interoperability, and cross- and intra-domain reuse of assurance assets. AMASS results were applied in 11 industrial case studies to demonstrate the reduction of effort in assurance and certification, the reduction of (re)certification cost, the reduction of assurance and certification risks, and the increase in technology harmonisation and interoperability.