How’s this related to the original game? As in licensing issues?
Idk about 2006scape, but I can tell about 2009scape.org. The server is fully FOSS and AGPL-3.0 licensed. No code from the original game is present, it's all rebuild.
The client is different and a bit more difficult, there is a project that's decompiling and deobfuscating the original client from around that time. It's not FOSS because it can't be, it's not their code to relicense, they don't own it. However it existing makes it possible for an alternative fully FOSS client to be created, as the internal workings of the original client is then known and documentation can be written about it. That way the new client developers can develop the new client without having to look at the original code, they just have to look at the documentation written based on that original code.
An alternative client like that hasn't been developer so far though sadly, I believe the community is more focused currently on the server-side and deobfuscating the original client.