HDOS has released their RuneLite plugin system into open beta. If you don’t know this client is a recreation of the 2009/2010 era client that contains the original HD update released in 2008.
The developers have also “remastered” several OSRS exclusive regions to be correctly textured and have that classic HD look.
Sadly if you’ve converted over to a Jagex account you cannot use this client yet. While it’s an approved third-party client it has not as of yet been added to the Jagex launcher.