声明型许可证 | Permissive Software License
对软件的使用、研究、修改和再发分上只有最低需求(minimal restrictions) ，常常只包含免责声明(warranty disclaimer) ，但这种许可证不保证派生版会继续保持自由软件形式。
与限制型许可证的区别：
- 声明型许可证，衍生版本许可证可能变化，但要保留原始版权声明
- 限制型许可证，需保持与原始许可证一致
Copyleft licenses generally require the reciprocal publication of the source code of any modified versions under the original work's copyleft license. Permissive licenses, in contrast, do not try to guarantee that modified versions of the software will remain free and publicly available, generally requiring only that the original copyright notice be retained. As a result, derivative works, or future versions, of permissively-licensed software can be released as proprietary software.
限制型许可证普遍要求修改后的互惠型作品的源代码版本使用相同限制型许可证。作为对比，声明型许可证不保证修改后的软件版本保持自由和开放，只要求保留原始版权声明。因此限制型许可证下的软件，其衍生作品或者后期版本是可以闭源发布成专有软件的。
[Source]
| MIT License | Apache License | BSD licenses | |
|---|---|---|---|
| 简称**SPDX** ****ID | MIT | Apache-2.0Apache-1.1Apache-1.0 | BSD-3-ClauseBSD-2-Clause... |
| 2021年前使用最多，目前top 2 | 目前top 1 | 目前top 10 | |
| 软件 | X Window System, Ruby on Rails, Nim, Node.js, Lua, and jQuery | Apache Project ListApache HTTP Server, Airflow, Hadoop, Hive, Spark, Flink, Kafka | BSD licensed softwareDjango, Go, D3.js, Chromium, Celery, Caffe |
| 公司/组织 | Microsoft (.NET Core), Google (Angular), and Meta (React) | Apache Software Foundation (ASF) | ... |
| 备注 | 很多非ASF的项目也是用Apache许可证，比如来自Linux Foundation中的项目 | - Go BSD-3-Clause + patent- Chromium BSD and others |
Bonus：与Apache Software Foundation(ASF)影响力同样巨大的是Linux Foundation(LF)，其陆续衍生出垂直领域的基金会，如Cloud Native Computing Foundation(CNCF)、LF Edge、LF AI & Data、GraphQL Foundation和近期才成立的eBPF Foundation。
弱限制型许可证 | Weak Copyleft Software License | Weakly Protective Software License
| GNU Lesser General Public License | Mozilla Public License | |
|---|---|---|
| 简称**SPDX** ****ID | LGPL-3.0+LGPL-3.0LGPL-2.1+LGPL-2.1LGPL-2.0+LGPL-2.0 | MPL-2.0MPL-1.1MPL-1.0... |
| 软件 | LGPL licensed software7-Zip, FFmpeg, GLib, GTK, Libheif, Qt, VLC media player | MPL licensed softwareBugzilla, Firefox, LibreOffice, Thunderbird, RabbitMQ, Terraform, Eigen, Brave Browser |
| 公司/组织 | Free Software Foundation (FSF) | Mozilla Foundation |
限制型许可证 | Strong Copyleft Software License | Strongly Protective Software License
| GNU General Public License | GNU Affero General Public License | |
|---|---|---|
| 简称**SPDX** ****ID | GPL-3.0-or-laterGPL-3.0-onlyGPL-2.0-or-laterGPL-2.0-onlyGPL-1.0-or-laterGPL-1.0-only | AGPL-3.0-or-laterAGPL-3.0-only... |
| 软件 | GNU, Linux kernel, GCC, GIMP, VLC, OpenJDK, GNOME | AGPL licensed softwareAnki, BDB, Grafana, MongoDB* |
| 公司/组织 | Free Software Foundation (FSF) | |
| 备注 | VLC uses both weak and strong copyleft | *MongoDB dropped the AGPL in late-2018 |
Weak & Strong Copyleft
-
Copyleft许可证都要求衍生版本使用同样许可
-
Strong Copyleft许可证要求衍生版本继续开源且使用同样许可
-
Weak Copyleft许可证在特殊情况下可以不遵守上述第2条规定
- LGPL应用在library上时，使用该库的软件可以是其他许可，不用跟着开源。（实际上LGPL中L最早为Library之意）
- MPL只有现有文件的修改才需要使用同样许可
Broadly speaking, the scope of the MPL, LGPL, and GPL can be summarized this way:
- MPL: The copyleft applies to any files containing MPLed code.
- LGPL: The copyleft applies to any library based on LGPLed code.
- GPL: The copyleft applies to all software based on GPLed code.
