As a developer tools analyst, I've compared Project A, cortexproject/cortex, and Project B, questdb/questdb, focusing on momentum, community size, and apparent use cases for the benefit of senior engineers. In terms of momentum, both projects exhibit similar recent activity, with 10 stars each over the last 30 days. However, QuestDB (Project B) boasts a significantly larger community, evidenced by its 16,789 stars compared to Cortex's 5,767. This substantial difference in overall star count suggests QuestDB has broader recognition and potentially a larger user base. Regarding use cases, Cortex is positioned as a horizontally scalable, highly available, multi-tenant, long-term solution for Prometheus, indicating its primary use is enhancing and extending Prometheus capabilities for large-scale, multi-user environments. In contrast, QuestDB is marketed as a high-performance, open-source time-series database, implying its use cases are more generalized towards time-series data storage and analysis, potentially attracting a wider range of applications beyond just Prometheus integration. The community size difference may influence support and contribution rates, with QuestDB's larger community potentially offering more extensive support and faster issue resolution. Conversely, Cortex's more specialized focus might attract deeper expertise in Prometheus-centric challenges. Senior engineers should consider these factors based on their specific project requirements, whether they need a robust Prometheus extension or a versatile time-series database.