Airtable - Airtable works like a spreadsheet but gives you the power of a database to organize anything. Sign up for free.
4D - 4D is a relational database management system and IDE.
Ragic - World's most advanced online database engine. Build powerful online databases with simple Excel style online interface.
LiveCode Platform - It is Both Under the GPL and it is also Proprietary if using the GPL version the software you make...
Knack - Knack is the easiest, most spectacular business management software available.
Informix - IBM Informix is a secure embeddable database optimized for OLTP and IoT data. Informix can seamlessly integrate SQL, NoSQL/JSON, and time series and spatial data.