Stavros from TileDB, Inc. here: Arrow employs a columnar format to store objects like data frames. TileDB is also columnar (so you can sub-select attributes and perform analytics with very similar optimizations to Arrow), but the first-class citizens are (the more general) dense and sparse multi-dimensional arrays. Moreover, TileDB focuses on optimizing for the persistent storage backend, so that it can handle out-of-core analytics on massive datasets that cannot fit in main memory (e.g., genomics), or offer the same performance using less RAM (leading to cost savings in the cloud). Nevertheless, we are quite fond of Arrow, so we hope to work together at some point and integrate as seamlessly as possible.