Multi-agent systems pair autonomous AI agents with marketplaces, orchestration frameworks and—increasingly—agent-to-agent payment rails to enable coordinated, composable workflows. This topic covers the technology stack and ecosystem that let agents discover, transact with, and delegate work to one another: agent marketplaces and registries for listing capabilities; agent frameworks and engineering tools for building reliable, stateful agents; and decentralized infrastructure for identity, micropayments and settlement (for example, platforms such as Fetch.ai’s ASI:One and peer offerings). Practical building blocks include marketplaces like Agentverse for deploying and listing agents; no-code entry points such as AgentGPT for quick agent prototyping; engineering frameworks like LangChain (and its stateful orchestration components) and LlamaIndex for retrieval-augmented document agents and workflow orchestration; and developer-focused IDE/agent environments such as Windsurf, Warp and JetBrains AI Assistant that embed agentic workflows into developer flows. Open-source, self-hosted options such as Tabby address privacy and local-first deployment needs. The converging trends driving relevance are: increasing demand for agent composability (chaining specialized agents rather than monolithic systems), the need for reliable state and evaluation in production agent apps, and emerging economic models that let agents negotiate and pay for services via micropayments or tokenized incentives. Key challenges remain interoperability, secure identity and payment settlement, governance and measurable safety/evaluation. Understanding how marketplaces, frameworks and decentralized payment rails interoperate is essential for organizations building scalable, auditable multi-agent applications and for evaluating trade-offs between centralized convenience and decentralized assurance.