Windows 98 is described as 'The best MS-DOS Windows Operating System released by Microsoft. Nowadays many players of abandonware still miss this rather stable and innovative OS' and is a operating system in the os & utilities category. There are more than 25 alternatives to Windows 98 for a variety of platforms, including Linux, BSD, Windows, Self-Hosted and Mac apps. The best Windows 98 alternative is Linux Mint, which is both free and Open Source. Other great apps like Windows 98 are Ubuntu, Debian, Fedora and Arch Linux.
As ReactOS is still in alpha stage and not suitable for everyday use, it is not very good alternative. But if you have some legacy (maybe customized or abandoned) software / game that require Windows 98, you should try React OS - it may work well and you will run your software in modern, supported OS.