What's in OpenTTD that wasn't in the original Transport Tycoon Deluxe?

OpenTTD is modeled after the original Transport Tycoon Deluxe game by Chris Sawyer and enhances the game experience dramatically. Many features were inspired by TTDPatch while others are original. You have also here a Comparison of OpenTTD and TTDPatch features.

Significant enhancements

• Multiple ports - A native Linux version, Windows, Mac OS X, OS/2 and more.
• Autorail build tool - Lets you drag and drop rail in any direction and the computer will build the tracks in that direction for you.
• Bigger maps, up to 4096x4096.
• Realistic scenarios based on heightmaps using digital elevation data downloaded from Google Earth, the forum page http://www.tt-forums.net/viewtopic.php?f=29&t=27052 or an up-to date word doc http://www.tt-forums.net/download/file.php?id=92633 .
• Canals/Locks - Allowing players to create waterways which stretch over the land and have ships navigate them.
• Larger stations - Stations can be longer, consisting of many more platforms.
• Non-uniform stations - Stations can be built slightly offset.
• Ability to join stations (of same width or length) - Building a station next to another station of the same type, width and lengths creates a single longer station.
• Waypoints - A special piece of track which can be placed on branching routes to force a train to use a particular branch to reach its destination.
• Mammoth trains - Trains can be much longer.
• Multi-headed trains - Trains can have more than one engine to help increase the speed when carrying heavy loads, power up hills etc.
• Build on slopes and coasts - It's possible to build on the slopes of the coastline or hills; the relevant tile is filled to a flat height for a certain cost.
• Goto depot order - Allows insertion of an order instructing a vehicle to return to the depot.
• Longer bridges - Bridges can span greater distances... at a price.
• Higher bridges - Bridges can span over greater heights enabling more complex networks.
• Three new bridges - To enable greater use of the higher speed trains.
• Presignals (CTRL-click on existing signals) - As TTDPatch - special signals to aid building complex track layouts (usually used when there are many platforms connected to a single train line).
• Semaphores (CTRL-D to place them) - As TTDPatch.
• Order sharing and copying ("goto" on other vehicle to copy, ctrl+"goto" to share) - Vehicles can now share orders with order changes propagating to all vehicles, and orders can just be copied by clicking on any other vehicle to save time.
• TTDpatch-compatible Non-stop handling - Exactly as it says on the tin.
• Crossing tunnels - Tunnels may now cross over each other underground.
• Build many trees on one tile.
• Bribe the town authority - If your townsmen hate you, you can bribe the local authority to help you but it's expensive and runs the risk of you being caught.
• Much improved networking and internet play by TCP/IP, including server lists, kick/ban, dedicated server, cheat protection and chat.
• AI framework allowing for new, user made AIs. The old (cheating) AI was removed.
• Several new types of airport (metropolitan in 1980, international in 1990 and intercontinental in 2002).
• Drive-through Road Stops - New kind of station for road vehicles. Much like a traditional real-life "bus stop", these new stations allow road vehicles to load/unload passengers and cargo simply by stopping by the side of the road.
• Tramways - New kind of road vehicles (like bus) and require special tracks, stops and depots for them.

Better usability

• Convert rail tool (to rail, monorail, maglev) - To enable you to easily switch your tracks to the latest technology.
• Build stations with drag & drop - Rather than guess at the size or count the tiles, just drag and drop the station over the desired area and it is built for you.
• Build while paused - An optional patch that allows building while the game is paused.
• Mouse wheel can be used to scroll in menus and to zoom in/out.
• Autoscroll (to left/right) - when you reach the edge of the screen, it moves across.
• Bigger demolish tool.
• Plant trees on area.
• Sell whole train by dragging to dynamite trashcan - Sells the whole train instead of just a single carriage.
• Cost estimation with Shift - Holding Shift on almost any action will show you how much it will cost you before you do it.
• Road and rail removing by dragging.
• Company HQ can now be moved somewhere else (cost 1% of company value).
• Autosave at a regular interval.
• Autorenew/replace vehicles that are nearing their end of life.
• It's now possible to remove a platform from a station by clicking on the station tool and then on the remove tool, then on the platform you want to remove.
• All TTDLX save games are supported (.SS1, .SV1, .SV2, .SV0, .SS0).
• High score table
• New pathfinding algorithm for trains.
• Landscaping.

New options

• "No train service" option.
• Disable inflation option.
• Full load any option, as in TTDPatch - Your train will leave the station if ANY of its cargos are full.
• "Select goods" option.
• "Multiple similar industries in close proximity" option.
• "Multiple industries per town" option.
• News item for "train is unprofitable".
• News item for "train is lost".
• Ability to set the starting date, takes a value on the form yyyy, yyyymm or yyyymmdd.
• Select what vehicle types the AI will build.
• Ability to choose snowline height.
• Change default servicing interval for vehicles.
• Change maximum number of vehicles per player.
• Option for percent-based service intervals. Send a vehicle to depot after it has lost X% of its reliability

Graphical/interface features

• Screenshots can be BMP, PNG or PCX (select in game options menu).
• More currencies (including Euro introduction in 2002 and your own custom currencies).
• More townname languages.
• Windowed mode or fullscreen including resolution selection.
• Sticky windows (don't close unless you close them yourself) and snappy windows (windows align themselves against each other when dragged).
• Resizeable windows.
• Refresh rate configuration setting.
• Town directory sorting.
• Advanced Settings configuration window.
• Use Ctrl-click to repay full loan or take out full loan.
• Color newspaper after a certain date.
• Game speed increase (through fast forward button or by pressing Tab).
• Plant a random tree type.
• Hotkeys for almost every action.
• Translations into a multitude of languages, selectable in-game at any point.
• Loading new graphics sets.
• Bring up an extra viewport showing any part of the map.
• Color-coded vehicle profits.
• Invalid orders in a vehicle's schedule are highlighted in red and generate a warning.

For details of every change, see OpenTTD