Mapnik is what runs the main OSM website, so I've used that, and I'm pretty sure I've used someone's website built on Tileserver, but I can't remember the details. In both cases I have no idea how much RAM or CPU the server side requires. I have vague memories I maybe tried JOSM once.

I also find OsmAnd~ very useful but I am often frustrated with both its slowness and its interaction design. I wish I had something better.