This release has significantly improved performance and further reduced resource usage even though mrxvt's footprint was already very small. New features include but is not limited to: better and intelligent tabbar apperance, full screen mode, new powerful macros (replacing hotkeys), XRender alphablending, popup menus, etc. Numerious bugs have been fixed as well. Please test it out and send us bug reports, comments, suggestions, and of course patchs.
Read the full changelog at http://materm.sourceforge.net/docs/ChangeLog-0.5.0