PlayFKiSS 2, aka PKFS2, aka PKFS0518 (most recent beta) by Chad Randall
(pkfs0518.zip)

The last PlayFKiSS version, incorporating the first set of FKiSS4 commands (defined in 2000) and as much of an editor as a viewer, including windows to trace FKiSS syntax and variables, a cel browser and a BMP import wizard. This viewer was never finished and, as such, is extremely buggy, but I've found it quite valuable both as a viewer (with the right workarounds) and as a coding tool.

Archive support: internal
FKiSS: 4 (not all syntax)
CKiSS: yes
Enhanced palette: yes
Bugs and idiosyncrasies:

I still haven't made a list of all bugs, or retrieved the author's own list of what hasn't been inplemented yet. Most importantly:
- Collision detection is iffy, and letcollide() and letinside() don't work.
- unfix() isn't triggered.
- There's hiccups with the attachment syntax: when switching to another page, objects with attachment syntax may be repositioned.
- Not a bug but nonstandard (although implemented before the standard was laid down): "keyrepeat", ie. the viewer interprets constant pressing of a key as a series of keypress() events.
- Not a bug, but different from older viewers: commands are applied to all ambiguous cels, so "unmap("image.cel")" unmaps all instances of that cel, not just the first one.
- Not a bug, but non-standard; the viewer has a default palette which it applies to any cels that need a kcf but haven't been assigned one.

Click here for a screenshot.