A lot of effort put into "dumb" text editors, but we still don't have (to my knowledge at least) a truly cross-platform / cross-backend IDE that will allow you,

A lot of effort put into "dumb" text editors, but we still don't have (to my knowledge at least) a truly cross-platform / cross-backend IDE that will allow you, for example, to open .sln/.cmake/.make/whatever projects/solutions and provide you with a nice interface to change project settings or even compiler used. This could save a lot of development time and improve productivity, and I'm sure it's a much more useful and common use case than collaborative editing.