ConciliaTower

A native Linux port of SimTower (Maxis / OpenBook, 1994), written fresh in C + SDL2. All of the game code is written from scratch. The mechanics are reimplemented to match the original's behaviour — their rules, thresholds, and timing constants reverse-engineered by studying a Ghidra decompilation of SIMTOWER.EXE and the YootTower code map. No original code or data is extracted from or executed out of the binary; the only thing read from the EXE at runtime is its art and sound.

Built by Claw 🦞 — an autonomous AI agent (Claude), running on a Raspberry Pi 5 in Berkeley. The reverse-engineering, the decompilation analysis, and every line of code in this repository are its work.

The goal is a faithful reproduction of the original mechanics — population growth, tenant satisfaction, elevator dispatch, star ratings, the disasters — running natively on Linux, using the original game's own bitmaps and sounds.

Play it in your browser

→ kvetch.io/conciliatower (mirror: jonahss.github.io/concilia-tower)

The story of how it was built: A complete and faithful SimTower remake, playable in the browser.

The same engine, compiled to WebAssembly. Bring your own SIMTOWER.EXE — it is parsed entirely in your browser (there is no server) and remembered locally, along with your saves. The page checks the file's structure and tells you exactly what to fix if you picked the wrong thing; see docs/SUPPORTED-BUILDS.md for the builds we recognize and how to report a new one.

Screenshots

Imported original towers, rendered live by the port using assets read from SIMTOWER.EXE:

Note on assets: this repository contains no copyrighted Maxis content. No sprites, sounds, or the original executable are distributed here. To run the game you must supply your own copy of SIMTOWER.EXE, from which sprites and sound effects are read at runtime (nothing is copied out or redistributed). See Providing the original EXE.

What this port reuses vs. rewrites

Read live from your SIMTOWER.EXE at runtime — and only this:

• All bitmap / sprite assets — read out of the EXE's NE resource table
• All sound effects (WAV resources)

Reimplemented from scratch, matching the original's behaviour:

• Game mechanics: population, tenants, elevators, star ratings, disasters

• Magic numbers, thresholds, and timing constants

  These are our own C code, not taken from the binary. Their behaviour and constants were reverse-engineered by reading a Ghidra decompilation and the YootTower code map, then re-derived and verified against the original — see docs/ORIGINAL-BUGS.md and docs/OPENSKYSCRAPER-ERRATA.md.

Platform layer, written fresh:

• Rendering (SDL2 instead of WinG)
• Sound playback (SDL2 audio instead of WaveMix)
• Window management and input (SDL2)
• The NE-resource parser and DIB→surface asset pipeline (src/ne_resource.c, src/sprites.c)
• Save/load — a native quick-save, plus full import and export of the original SimTower 1.1 .TWR/.TDT format (src/twr.c), so towers round-trip and are interchangeable with the original game

Building

Requires a C11 compiler and the SDL2 development libraries.

# Debian / Raspberry Pi OS
sudo apt install build-essential libsdl2-dev libsdl2-ttf-dev

make            # produces ./simtower

Providing the original EXE

The game reads its art and sound directly from an original SIMTOWER.EXE every time it launches. You need a legitimately-obtained copy of the file — it is not included in this repository and never will be.

The binary looks for the EXE in this order:

1. A path passed on the command line:

   ./simtower /path/to/SIMTOWER.EXE
   

2. Auto-detected locations, relative to the working directory:
   • ./SIMTOWER.EXE
   • ./data/SIMTOWER.EXE
   • ../OpenSkyscraper/data/SIMTOWER.EXE

The simplest setup is to drop the file at data/SIMTOWER.EXE:

mkdir -p data
cp /wherever/you/have/SIMTOWER.EXE data/SIMTOWER.EXE
make run        # equivalent to ./simtower data/SIMTOWER.EXE

You can also point the Makefile's run target elsewhere:

make run EXE_PATH=/path/to/SIMTOWER.EXE

The filename match is case-insensitive on the resource contents, but keep the name SIMTOWER.EXE for the auto-detected paths to work.

If no EXE is found the game exits with:

Cannot find SIMTOWER.EXE. Pass path as argument.

Running

./simtower data/SIMTOWER.EXE

Optionally pass a tower file to load a saved game:

./simtower data/SIMTOWER.EXE mytower.tdt

On a headless machine (e.g. a Raspberry Pi), scripts/launch.sh starts the game inside Xvfb and exposes it over VNC/noVNC — see the comments at the top of that script.

Layout

Documentation

• PLAN.md — architecture and the phase-by-phase build history (all six phases complete).
• docs/ORIGINAL-BUGS.md — a catalogue of the original SimTower's genuine bugs, kept separate from its surprising-but-intended mechanics. We reproduce the intended behaviour faithfully; the bugs are documented so we can decide case-by-case whether to preserve them.
• docs/OPENSKYSCRAPER-ERRATA.md — where the OpenSkyscraper reference implementation diverges from the original binary, verified against the decompilation.
• UI_TODO.md — the live worklist: remaining faithful loose ends and the mod-idea backlog.
• docs/REFACTOR-PLAN-runtime-model.md — the runtime-model refactor brief (completed and merged, June 2026).

Status

Playable end to end. All six planned build phases are complete (PLAN.md) — the port goes from an empty lot to the 5⭐ → TOWER win condition (cathedral, VIP, wedding ceremony) with the original's mechanics:

• Simulation — population and standing-population star thresholds, the EXE's banked felt-wait stress model with daily category passes, vacancy re-let, per-type economies (office tiers, condo sales, hotel booking demand with housekeeping/infestation, restaurant/shop patron flows and quotas, cinema show cycles), zone competition, VIP visits and promotion gates.
• Elevators — faithful placement rules, car state machine with the real tuning constants, queues and 3-strike wait stress, the original schedule dialog rebuilt on its own artwork (bitmap 0x8190) and the full-screen "Simulate" shaft-edit mode.
• Disasters — scheduled fires with per-floor fronts and the $500k helicopter, bomb threats with ransom/hunt, decision modals, rubble, alerts.
• UI — Win3.1-style menu bar, toolbox with pull-downs, minimap overlays, tenant/venue info dialogs, the quarterly financial report on the original 0x81f4 artwork, campaign (star-gated) and sandbox modes.
• Interchange with the real game — original 1995/96 .TWR/.TDT towers import, play, and export byte-identically.
• Tests — a 320-check SDL-free simulation suite (tests/test_sim.c).

Remaining loose ends are small and tracked in UI_TODO.md: shop closed/for-rent storefront frames, the elevator dialog's 24px mode-icon art, a couple of unwired sound effects, and a reader for the EXE's dialog string table (event text is currently hardcoded to matching wording). A backlog of deliberate, clearly-labelled mods (multi-tower bridges, window-washing cranes, …) lives there too — the faithful base stays clean.

Legal

This is a clean-room-style reimplementation of the game's code. It ships no Maxis assets and no original executable. SimTower is © its respective rights holders; you must own a copy to supply the SIMTOWER.EXE this port reads at runtime. This project is not affiliated with or endorsed by Maxis, OpenBook, Vivarium, or any rights holder.

src/vendor/mspack/ contains a minimal subset of libmspack (© Stuart Caie, LGPL 2.1), used to expand the MS-Compress SIMTOWER.EX_ found on original CD/floppy media. See src/vendor/mspack/README.md.