It's LGPLv2+ which doesn't restrict your use in any way — you can combine it with proprietary code, ship it in closed source products etc — but does mean that you must contribute changes (to this library code only) back rather than being able to steal them from the commons for your proprietary benefit.

It's a cool unnamed product you work on, but being proprietary means that it's useless for any project I've ever worked on.

Did you actually think that anyone could possibly sympathize with a complaint about the intolerability of reciprocity?

Whatever product you're working on, if it can't include any gpl code, then it means they give you money instead. Do you hear yourself? "Boo hoo I can't take without giving" ?

Or are you claiming that you have only ever worked on MIT projects?

No license is going to be suitable for everyone. You might think BSD, MIT, WTFPL are the most liberal licenses but they are not suitable for me. If I am invested in an open source software enough to contribute code to it then I want that when a greedy company takes that software and improves it and redistributes it they are also forced to release the source code benefitting everyone. BSD, MIT, WTFPL can't do that but GPL can. No license is a silver bullet.

You’re free to contact the author to pay for a commercial license for your projects.

Good.

It's LGPL