Status: This has been implemented and will be included in the next update.
Slight flickering when changing between screens in windowed mode is a known issue, and this will require significant changes to how NeoLemmix works in order to fix it. Therefore, I will not be fixing it for now.
Self-explanatory. An often-requested feature is to support windowed mode as well as fullscreen.
Good news for all the people who wanted this - I'm getting VERY close to a successful implementation of it!
There's two minor bugs remaining:
1. It's possible to scroll a short distance beyond the right edge of the level (showing an empty white space), unless either you're in full screen, or in windowed mode at the highest zoom setting your screen resolution can support. The lower your zoom setting, the further beyond the edge you can scroll. (TODO: Check if this happens with the bottom too, for levels with vertical scrolling.)
2. If NeoLemmix is in full screen mode and the setting has been changed since NeoLemmix.exe was started, the desktop is briefly visible between screens.
I have no idea what's causing #1 yet I've fixed #1 now. I have a rough idea of what's causing #2.
Implementation and fixing the errors around it is done. From the next update (V1.37n-B or V1.38n, whichever it ends up being), NeoLemmix will support windowed mode. :)