I am 99.9% sure that the version you are referring to is Dan Richardson's excellent JSWII remake for the PC (or, to be precise, one of them - please see below). In fact, I believe (without checking it in detail) that Spider has given links to this very version. If you don't think it's the one you remember, I think your memory is playing tricks on you.
The reason I say it is because:
- I think it's actually the only remake of JSW2 for the PC in existence;
- It *is* the one that came with a room editor, and I *really* doubt that there could have been another PC version with a room editor.
The remake and the editor were discussed on the Manic Miner & Jet Set Willy Yahoo! Group in the past. The actual original announcement of the level editor is here. The link there to Dan's homepage is dead, but perhaps you will have some luck looking it up on the Wayback Machine if you choose to do so.
In the text file accompanying one of the releases I mention below, Dan says, "I originally released two previous versions of a Jet Set Willy II remake a while ago (...) You can find them at these two web pages..
These links are dead, but what I want to highlight here is that Dan apparently released two versions of a JSWII remake. So perhaps if the version which you can download from the link Spider gave does not look like the one you remember, it could be that you remember Dan's other version, if there were two of them. In any case, I am sure you do have a remake by Dan Richardson in mind.
The version which I believe was the final released one is here:
Below there are also some files which used to be hosted in the Files section of the Manic Miner & Jet Set Willy Yahoo! Group (not accessible any more). Among them is the first release of Dan's PC version, a test version of the Sprite Editor, a Mass Collaboration file (which never really took off, IIRC) and "JSW Remix", which is " basically Jet Set Willy with some screens from Jet Set Willy II and some extra screens" designed by Dan Richardson. Perhaps this is the one you remember.
I am not sure about the current status of these files. Please don't spread them excessively and do let me know after you have downloaded them, and I will delete them from here, just in case Dan wouldn't want them available for download at this time.
Enjoy and do let us know if any of these is what you remember and what you've been after!