> Specifically, a proprietary vendor can use and/or modify your GPL-licensed library on their server-side application and is not obligated under the terms of GP

> Specifically, a proprietary vendor can use and/or modify your GPL-licensed library on their server-side application and is not obligated under the terms of GPL to release any changes, so long as they never distribute the app. Sure but if it doesn't make sense to use that service remotely, then just use the FOSS one instead. If the expected behavior is that the software you are writing will be running on a computer the user directly interacts with and can physically touch, it's probably fine to use the GPL. Web services and web libraries are a whole different ball game but I'm not going to use a GUI, signals analysis/transform, data structures, CUDA, hardware interface, or other common local library if I have to call it over a network. Doubly so if I now have to fight with an RPC endpoint instead of a DSL or library in my native language. And when I say GPL, there are a handful of different flavors. I generally think GPL+linker/classpath is a fine choice for most projects that are geared towards commercial use. I'd say LGPL is fine too and it is but there are some small differences between GPL+LE/CPE and LGPL. So for the sake of simplicity, "just default to GPL unless you have a good reason to increase or decrease the copyleft-ness".