I think I'm done with this one, but not tested it too thoroughly.
It's fully working ferry wheel which can be used by up to 8 sims at the same time.

Usage instructions.
1. Use Turn On to start wheel rotation. Ride On action is available only when wheel is rotating.
2. Use Ride On to ride When selected, sim waits for the next free seat to be down, then sits into it, then rides until certain conditions, then waits until seat is down, then leaves. Conditions for stop riding are one of the following:
- user cancelled Ride On action
- sim's Fun is maximum
- sim's Energy or Bladder are too low
- another sim selected Ask To Free All Seats
While riding, sim's Fun and Comfort increase. Sim looks around at nearby objects - so make sure that there are objects around ferry wheel to make riding more realistic.
All ages except toddler can ride. Visitors can ride too.
3. Use Ask To Free All Seats when you want all sims on the wheel to get down. It may be useful, for example, if you want the visitors to stop riding.
4. Use Turn Off to stop wheel rotation. This action is available only when all seats are free.
Action autonomy values are changed so that sims are likely to use Ride On autonomously, while other actions are likely to be done by user's command only.

Uncertainties (need test).
1. I tested the wheel in Residential and Community (riding is free there) lots, but don't know what'll happen in addon-specific lots since I have no addons. Please inform me if there are problems with them.
2. Ride On should become disabled when all seats are used. However, I didn't seen it myself - my families are small and don't have enough inviteable friends to test it. If someone can test this condition, please tell me if something will go wrong.

Known bugs.
1. Please don't fill the tiles adjacent with ferry wheel with objects - they are used by sims waiting for their seat down, but I was lazy to add 'dummy' tiles for those - this object already used 7 GUIDs, I'd say it's enough for it.
2. You can build walls around the wheel and then put floor on second pace to 'slice' the wheel - please don't do so I can't figure out how to workaround it - standard tall objects like trees and tall lights have the same problem; I could create dummy tiles on 2nd floor, but, again, it would take more GUIDs for nothing.
3. While seating in/out, sims kind of go through the mesh - through the seat on adjacent tile. It's unavoidable with current geometry I count it as minor so didn't remesh.

General details.
Object is visible in the Neighborhood View - make sure that you extracted both files from archive for this.
Object has 2 recolorable subsets - 'metal' and 'other', 3 recolors available for each - and 1 non-recolorable subset, 'button', which color is red when wheel is stopped and green when wheel is rotating.
Object can be found under Hobbies/Recreation.

Technical details.
Mesh geometry:
- 'metal' subset - 1338 faces, 2042 vertices.
- 'other' subset - 352 faces, 704 vertices.
- 'button' subset - 22 faces, 16 vertices.
I'd say it's fairly low for an object which is 5 tiles long and 2 story high.
The 'lod90' object (used by neighborhood view only) has the same meshes for 'metal' and 'other' subsets, 'button' is absent there.
The object used as start for the ferrywheel was the Grandfather's Clock.
Mesh was created in 3ds max and imported using smd plugin.
Animations were edited in SimPE built-in plugin.

Thanks.
To skankyboy, for the smd plugin.
To Numenor, for explaining CRES structure.
To atavera: for explaining slot types and SLOT resource contents; for explaining footprint block structure; for finding silly bug in my Init function.
To fisheeyes, for explaining how to add slots to objects.
To Peter Jones, for PJSE plugins.
To Echo, for various BHAV-related information.
To quaxi, for SimPE and built-in ANIM editor.
To modthesims2 in general without the information from here, I wouldn't be able to make this object.

Policy.
Feel free to recolor, but please link back to this thread, and don't post on pay sites or as donation.
As for my permission first if you want to clone and remesh it.

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Changed on 09/21/2006.
1. The rule of motives increase is corrected.
2. New interaction, 'Ride On (No Motive Exit)' added - works the same as 'Ride On', but no motive test is made.
3. Attractiveness is (hopefully) increased.

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Added on 09/23/2006.
Looks like some people can't download updated version; I'm trying to attach the same archive with different name.
In case it still wouldn't work for someone, try to get the file here.