Are there any open-source Esri map viewer equivalents that you recommend?

jamaykans

I’m Working as an intern for a non-profit that has a need to present their geospatial data on their website.

I frequently see websites with a data viewer that looks to be hosted in Esri Mapviewer. I think I could possibly learn the tool, but given I work at a non-profit which is on a tight budget, I’m curious what kind (if any) free/open-source tools exist out there that are worth investing your time in.