There are a few, from freeware, shareware to licenced USB-dongle:
Freeware
Multiscreener from https://www.zachpoff.com/software/multiscreener/
– basically Mac. Windows version available but…
– uses Quicktime player
Shareware
Video Mill from https://breakthrusoftware.com/html/products/videomill/index.html
SyncMaker Pro from https://www.syncmaker.com/
Licenced USB-dongled
Dataton Watchout 5 – minimum 2 licences required, 1 for Production Pc, 1 for Display PC which can output to max 6 outputs, hardware permitting
AvStumpfl Wings Platinum 4 – minimum 1 x 3-output licence required (actually comprising 1×2-output and 1×1-output licence, or 2×2 output licences; Application window/monitor is not part of the Output licence, eg. App monitor + 1xfullscreen Output is the 1-output licence, etc. (PM me privately for more details of how this works.)
Above are for Windows PCs. There are solutions for Mac too which others may be able to point you to.
Recommended hardware-based solution is the Ethernet capable Brightsign units (HD210 – now HD220?) from https://www.brighsign.biz using their free BrightAuthor software to author the SD cards with your 3 different video files (must be same file-length) to playback together.
Thomas Leong