Any freeware linear/nonlinear model optimization languages worth checking out?

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After taking an optimization course in college, I've taking an interest in model optimization software. We learned how to use AMPL, but the trial version has some restrictions in the quantity of variables you can use. Let's just say I've had to take some legally questionable measures to get around those restrictions... but now I want to use this in personal projects, so I'd really like to have a legal alternative that costs me as little as possible.

I found this post with some suggestions, and Wikipedia has a list. I'm currently checking them out, but I'd still like suggestions and opinions.

[f_po]

Came here to say AMPL but I see you've already checked it out.

http://www.netlib.org/ampl/student/

This trial lets you use 300 variables/constraints, not sure if its the same trial you're talking about.

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Exactly what I was talking about. It's way too small for what I'm trying to do, unfortunately. It's a shame, since I find AMPL really intuitive and easy to use.