Emuos.v1.0 [portable] -

You may be referring to one of these:

Beyond gaming, it serves as an educational tool to demonstrate how early computing environments functioned. emuos.v1.0

One of the biggest complaints about web emulators is that you lose your work on refresh. implements a virtual hard drive (VHD) system stored in your browser’s local storage. You can create a text file in Windows Notepad, save it to "C:\MyDocs," close your browser, and reopen it days later. The file persists. You may be referring to one of these:

7 Stability (1–10): 8 (crashes rare, but ROM compatibility varies) Documentation quality: Sparse but sufficient for Linux-literate users. save it to "C:\MyDocs

Entirely web-based; accessible via modern browsers on desktop and some mobile devices.