Lib

https://www.google.com/search?q=best+cross-platform+GUI+toolkits

pyqt

pip install PyQt5

QNetworkProxy

https://doc.qt.io/qt-5/qnetworkproxy.html

Apps

Browser

qutebrowser

Install: https://github.com/qutebrowser/qutebrowser/blob/master/doc/install.asciidoc#manual-install
Windows + tox + conda: https://stackoverflow.com/questions/30555943/is-it-possible-to-use-tox-with-conda-based-python-installations

Proxy Types: https://github.com/qutebrowser/qutebrowser/blob/86fca3e99ee4836f5f591831eb93a09ffb8231d2/qutebrowser/utils/urlutils.py#L599

admbrowser

https://github.com/alandmoore/admbrowser

HTTPS, FTP, SOCKS, or authenticated proxy is not currently supported