There are many options for scan doubling the output from our retro computers to utilize a modern monitor. Among them is the Gonbes GBS8200. It is certainly not the best option, but, for those on a budget, it will do. I recently purchased one to put into my DIY arcade cabinet that houses a CAPCOM CPS2 system board with a DarkSoft multigame board (plays every single capcom CPS2 game by removing the original ROMs and replacing them with a board that fits into those sockets and can be flashed at will to change games). The stock results were OK, but, there were plenty of artifacts and it was somewhat lagged.
Enter GBSCONTROL firmware:
It requires getting and ESP8266 WiFi development board, flashing it with Arduino IDE, soldering it to several key points on the board, and optionally soldering an external clock generator board to eliminate any screen tearing. All in, it costs under $30. The results are amazing. You control the scaler via WiFi from any computer browser, as the ESP module now provides a webserver for you to connect to at http://gbscontrol. Simply connect to the wifi point, login with the password of qqqqqqq and you're set.
I am no video aficionado, but, I can't see any lag. You can add scanlines if you prefer, and vary them in strength according to your preferences. There are many other options to play with on GBSCONTROL, as well as others in development. It took me about an hour tops to build, and I am glad I did, versus buying a second OSSC for $200.