Icaros' approach to old applications is fairly different than the one chosen by PPC-based operating systems like AmigaOS 4.1 and MorphOS 3. Due to the completely different x86 architecture, it needed to choose the road of emulation, providing a complete M68K Amiga virtual machine which runs another session of AROS itself, compiled for the Motorola 68000 processors. Since both host and guest systems are running AROS, they can share user settings for input methods, language, fonts and many other graphic details of the interface, making classic applications appear perfectly integrated in the AROS system. This, at least, in theory: there are still some glitches with right menus in coherency mode, but they can be easily worked around running the emulation layer on its own "screen", like most Amiga applications did in the past.
Lovers of AmigaOS 3.X, however, can still integrate the original OS into Icaros to gain perfect compatibility with the past, but they will have to provide files by themselves, eventually buying a copy of Cloanto's Amiga Forever.
Icaros Desktop 1.5 also changes the installation procedure, allowing people to exclude from their hard drives unwanted categories of software. For instance, if they're running Icaros without a supported 3D graphics card, they can now choose not to install games which need hardware acceleration. Icaros Desktop is now based on a new AROS kernel but, in case of compatibility issues, it also provides a "Legacy Kernel Edition" to use in the meanwhile, until all regressions will be fixed.