The GPL License is the most famous copy-left kind of license. ChibiOS is free under this license and can be freely used and redistributed under its terms.
The product licensed under GPL3 is complete and unrestricted.
ChibiOS is also available onder GPL3 with a linking exception that makes possible to link proprietary code to ChibiOS without being “infected” by GPL3 viral clauses, this means: no need to disclose the proprietary source code. All other GPL3 clauses still apply.
This version has limitations:
Some parts of ChibiOS are licensed under the Apache License 2.0. This license places less restrictions on the user and allows for free commercial use. Non critical parts of ChibiOS are released under this license.
Features comparison and use cases.