You can find a thread about it here on Hack64: Features It is an all-in-one tool that has both a level importer and an object editor.
If you want an alternative to Quad64, then I'd recommend using Pilzinsel64's SM64 ROM Manager. The source code will still always be avaliable and open source for anyone to look at and use for any reason. I do not have any kind of motivation to work on this project anymore, so this branch will no longer recieve any updates. This project is no longer offically being worked on.
An open-source SM64 level editor written in C# 4.0, and uses Windows Forms and OpenTK.
