The native look and feel is important and is also addressed in the current JDK 1.6 release.
But with Swing it is also very easy to switch the L&F, event afterwards. It is enough to provide the system property -Dswing.defaultlaf= to change it. There is a new L&F called nimbus with a webstart demo. It looks great (event better than substance :-)).
Web Apps, SPA, PWA with vanilla Java Script (ES 6+), CSS 3 and WebStandards only. As simple as possible, but not simpler. See you at: (Progressive) Web apps, Single Page Apps and WebStandards airhacks workshops at MUC airport, Winter Edition
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