ULTERA database, developed under the ARPA-E's ULTIMATE program, is aimed at collecting literature data on high entropy alloys (HEAs) to facilitate rapid ML-based discovery of new ones using forward and inverse design. The main scope of this dataset is collecting data on compositionally complex alloys (CCAs), also known as high entropy alloys (HEAs) and multi-principle-element alloys (MPEAs), with extra attention given to (1) high-temperature (refractory) mechanical data, (2) phases present under different processing conditions. Although low-entropy alloys (incl. binaries) are typically not presented to the end-user (or counted in statistics), some are present and used in ML efforts; thus, all high-quality alloy data contributions are welcome! You can set up a contribution in as little as few minutes with this contribution repository at contribute.ultera.org As of July 2023, ULTERA contains over: 6,830 property-datapoints, corresponding to 2,850 unique HEAs, collected from 536 unique DOIs. All data is available through a high-performance API, following FAIR principles, while statistics on it can be found at our ultera.org project web page. The database architecture is designed to automatically integrate starting literature data in real time with methods such as experiments, generative modeling, predictive modeling, and validations. Beyond large size, ULTERA has further advantage of being highly curated with many steps of data validation and then processed through our abnormal data detection tools (pyqalloy.ultera.org).