This is a 1998 Riven calendar that was available by mail-order from a catalog that shipped with some big-box copies of Riven, for a price of $7.95.
This calendar is smaller than the two Myst wall calendars from 1996 and 1997, measuring 9" wide by 12" length when opened. Each month features a high-quality render of a Riven screenshot as the main art, plus a small render of a Riven prop in the bottom right corner. Notably, this calendar lists both normal surface holidays (such as Labor Day) as well as several notable D'ni dates (which are not all D'ni holidays).
The calendar is constructed from 7 sheets of card paper which are folded in half and joined by staples. As a result, the renders are not printed on the same sheet of paper as their corresponding month. These scans have been rearranged to correct this, but due to the warping of the pages, the edges of the sheets don't stitch together perfectly. Since there aren't any elements that span between the two pages anyway, I haven't tried to correct these seams. June, being the month that spans the innermost page, is the only month that is intact, leaving the original seam visible in the scan.
Cover (5500 x 7350, 19.2 MiB)The cover features a large close-up of the Wahrk. The back cover contains the Cyan Productions logo, the UPC, a legal disclaimer, and a link to riven.com.
Inside cover (5500 x 7350, 25.48 MiB)On the top of the first page is a small version of the "5" symbol from Riven's main menu. The bottom is the door from the village on Jungle Island. Considering that the color balance is wildly different and the door-knocker is missing, this is probably just a photograph of the same prop.
January (5500 x 7350, 18.21 MiB)The top image is a render of the "northwest path", though the model of the plant is different and is visibly clipping into the railing. On the bottom is a render of one of the maglev vehicles.
February (5500 x 7350, 16.8 MiB)The top render is an often-used image of the village. This appears to be the same render as the jVillageWired.3125 that appeared in the Riven Pre-Release Screenshot CD, which has some small changes to hut shape and walkway placement compared to in-game. On the bottom is a render of the submarine, which happens to be the place in-game where this village render is visible.
March (5500 x 7350, 17.49 MiB)March features a render of survey island. Some touchups are missing from where the rocks meet the water, and the cliff face has a slightly different texture on the left. The render is also from a slightly different position. On the bottom is one of the lamps from the classroom, with the D'ni text visible, reading "t'Gehn pahneht" many times.
April (5500 x 7350, 14.62 MiB)The top render is from the Wahrk-viewing room on survey island. The central spire is higher than it should be, and there are many differences to the rocks that make up the natural cavern wall here. The bottom image is a top-down view of the sink in Gehn's bedroom from age 233.
May (5500 x 7350, 19.09 MiB)The top is the same render as the tSuperBridge render from the Riven Pre-Release Screenshot CD, with the same minor differences from the finished game version. The bottom image is the lamp from Gehn's bedside table on Age 233.
June (5500 x 7350, 15.18 MiB)June is the innerpost page, and so this scan shows the original joint between the top and bottom of the page. There are no discernable differences between this render of the boiler and the one in-game. The bottom image is Gehn's Maral-Obe, which hangs on the wall in Age 233.
July (5500 x 7350, 17.96 MiB)The top render is an exterior view of Prison Island with no discernable differences. On the bottom is the imager from the classroom.
August (5500 x 7350, 15.58 MiB)The image on August is an exterior view of Age 233 that isn't visible in-game. On the bottom is Gehn's pipe. These renders also appeared inside the booklet for the Riven soundtrack, specifically the cardboard-sleeved edition that was published by Virgin Records in 1998. I don't know if the jewel-case version of the soundtrack (appearing in the same catalog as this calendar) contains the same booklet or renders.
September (5500 x 7350, 18.09 MiB)September's main image is a shot of Gehn's desk from Age 233, from a slightly different position. On the bottom is the Wahrk-hanging game from the classroom that seems completely different from the one in-game. The Wahrk and prisoner are modeled differently, the mechanism at the top of the pole is designed differently and made of metal, and the Wahrk and water have been painted.
October (5500 x 7350, 13.58 MiB)Just like the "elevator" render from the Riven Pre-Release Screenshot CD, this render shows the elevator lowered and closed, which isn't possible in-game. On the bottom is the gold-painted Wahrk altar that sits beside the submarine's starting point.
November (5500 x 7350, 17.71 MiB)November's render of the boiler is almost identical to the in-game render, except for a kink in the pipe at the top-right and an extra brick foundation in the water on the bottom-left. The bottom image is one of the totems that sits next to the submarine and the Wahrk altar.
December (5500 x 7350, 15.48 MiB)This render of Tay is identical to the one in-game, except that the smoke on top is missing. On the bottom is an image of one of the Moiety daggers.
Given the number of small differences in some of these images, it's reasonable to assume that some of these renders are from before the game's geometry was finalized, and that they simply didn't bother going through the trouble of re-creating high resolution renders whenever they already existed.
These are the D'ni dates that appear on this calendar, plus their conversion into D'ni dates. There are differences between these dates and the D'ni timeline published by Cyan. Most notably, the Day of the Circle has been switched with the Sealing of the Great Temple. All of the other differences can be attributed to the fact that D'ni yahrtee do not correspond exactly to surface days, though these differences are odd considering that both timelines were presumably decided by Cyan.
Leevosahn 13
Leevotar 17
Leenovoo 10
Leenovoo 18 (Cyan's timeline puts this on Leefo 23)
Leefo 12
Leefo 23 (Cyan's timeline puts this on Leenovoo 18)
Leebro 20
Leesahn 8
Leetar 21
Leevot 8 (Cyan's timeline puts this on Leevot 9)
Leevot 11 (Cyan's timeline puts this on Leevot 12)
Leevot 22
Leevofo 7 (Cyan's timeline puts this on Leevofo 8)
Leevofo 17 (Cyan's timeline puts this on Leevofo 18)
Leevofo 27
Leevobro 11 (Cyan's timeline puts this on Leevobro 12)
Additional photos:
(2848 x 2134, 1.1 MiB)