FoundationDB is a key-value database that can be used to build new application-friendly databases, but it has several limitations and weaknesses when compared to other databases such as YugabyteDB. FoundationDB's architecture is complex, making it difficult for developers to understand and use, while its core engine seems to favor approaches that are architecturally limiting and reinvent the wheel in terms of high-performance storage engines. The database also lacks a SQL-compatible relational layer, has limitations in fault tolerance, and does not support multi-region active/active clusters. Additionally, FoundationDB's ease of use is hampered by the inability to easily introspect browse the current data managed by the cluster, and its command line shell is weak compared to other databases like YugabyteDB. Overall, while FoundationDB has some strengths, it misses the mark on making application development and deployment easier, particularly in comparison to databases like YugabyteDB that offer more flexibility, scalability, and ease of use for internet-scale transactional workloads.