There's jEdit. It looks horrible out of the box, but it looks as good, if not better than most modern editors. It runs on the jvm and so is sluggish to launch

There's jEdit. It looks horrible out of the box, but it looks as good, if not better than most modern editors. It runs on the jvm and so is sluggish to launch, but it's an extremely mature product and the plugin ecosystem is nice. Getting the latest plugins is a bit hit or miss, but it's worked great for me and my colleagues. Font rendering is awesome and has support for ligatures etc.