Demiath gets an Open Source Scan Converter
For some reason, I decided to get an OSSC - even though I don't actually own a lot of retro consoles to use it with (yet). Plugging in a Dreamcast I bought a few years back shows an immediate increase in picture sharpness, despite using the same old RGB cable as before and also being relegated to the only output mode my decidedly non-retro-friendly Elgato HD 60s capture device seems to recognize (Line2x).
The OSSC is technically not an upscaler - and is best used with older consoles than 6th generation stuff - but it does handle both my Dreamcast and PS2 better than my old HD TV did. And since my current 4K TV only has HDMI inputs, the OSSC or an equivalent solution was necessary to be able to use those consoles at all with my current setup.