amiga.democrat

The story of

Gravity Force

1989 · Kingsoft · Stephan Wenzler · Shooter · 1-2 players

Released	Early 1989 (reviewed in ASM and Power Play, May 1989) ^[9]
Design, code, graphics, sound	Stephan Wenzler (sometimes spelled Stephen) ^[14]
Publisher	Kingsoft GmbH, Aachen, Germany ^[3]
Players	1-2 simultaneous ^[14]
Platforms	Amiga; Wikipedia and MobyGames also list Atari ST and DOS (1989) ^[13]
Launch price	DM 39 (Power Play); about DM 40 (ASM) ^[11]
Missions	50 per Power Play; 49 per MobyGames ^[11]
ASM (5/89)	9/12 overall per Kultboy (graphics 7, sound 7, motivation 10) ^[10]
Power Play (5/89)	72% (Anatol Locker) ^[11]
Freeware re-release	1999, by the author, via Amiga Fever ^[9]
Sales	Not known ^[9]
Sequel	Gravity Force 2 (1994, fan-made, freeware and registered versions) ^[7]

The idea

Gravity Force is a cave-flying shooter in the tradition of Thrust. Your little ship can only rotate, thrust and fire; gravity pulls it down all the time, inertia carries it on after you let go, and touching the rock destroys it ^[1]^[11].

Alone, you fly missions through the caverns, picking up cargo crates and bringing them home to base while big enemy ships and gun emplacements shoot at you ^[10]^[11]. Heavier crates drag the ship towards the floor ^[11]. Power Play counted 50 missions on the disk ^[11]; MobyGames' description says 49 mazes, with a password after every five levels that lets you start from there ^[12]. There are also three race modes: a solo time trial over ten courses, each with eight numbered gates, a split-screen race for two pilots, and a two-player Dogfight ^[10]^[11]^[12].

Reviewers then and now agree that the two-player game is the heart of it and that the solo missions get a bit repetitive ^[6]^[10]^[11]. The author himself later admitted he had underestimated the two-player mode while concentrating on the traditional part of the game ^[9].

Who made it

The game is the work of one man, Stephan Wenzler, who is credited with the code, graphics and sound ^[14]^[16]. That is how he signed his own account of making the game in 1999 ^[9], and how MobyGames and the AROS remake spell it too ^[5]^[12]. Wikipedia, Lemon Amiga and the AmigaPD interviewer write "Stephen" ^[1]^[4]^[15].

In that account, written for the German magazine Amiga Fever, Wenzler says he was a 17-year-old with an Amiga 500 in 1988. He wrote the game in the Seka assembler and wanted to make something like Thrust. His first plan was to rescue little men, as in Choplifter, but he switched to collecting crates because that was simpler to program. He built the caves from 8x8-pixel blocks, an idea he took from the C64's character mode, and then added the race through numbered gates, the split-screen two-player mode and finally the Dogfight ^[9].

When the game was about 90% finished, he sent a demo to Kingsoft and two other publishers. Two said yes, and Kingsoft got the deal. The name "Gravity Force" was Kingsoft's idea; otherwise the publisher left the game alone ^[9]. Kingsoft was a company from Aachen in Germany. Fritz Schäfer founded it in 1982 to sell a chess program he had written. By 1988 it was putting more and more of its effort into Amiga games, which it sold for less than the DM 80 most Amiga publishers charged ^[3].

Release and price

Wenzler says the game came out at the start of 1989 ^[9]. The German magazines ASM and Power Play both reviewed the Amiga version in their May 1989 issues ^[2]. It was cheap, as Kingsoft's games usually were: Power Play listed it at 39 Mark and ASM at about DM 40 ^[10]^[11].

Wikipedia and MobyGames also list Atari ST and DOS versions from 1989 ^[1]^[13]. Neither gives a source, and ASM was still hoping for an ST version when it reviewed the Amiga game ^[10]. We found no review of either version.

In 1999 Wenzler got the game released from Kingsoft's copyright. He made a version that runs on all Amigas, not just the A500, and gave it away free through Amiga Fever ^[9]^[12]. How many copies the original sold is not known. Wenzler only remarks that the game did not make him rich ^[9].

What the press said

German reviewers liked the game more than they liked how it looked and sounded:

ASM (5/89), Jörg Heckmann: 7/12 for graphics and 7/12 for sound, but 10/12 for motivation and 9/12 for value for money ^[10]. Kultboy lists the review at 9/12 overall ^[2], and Wikipedia at 75/100 ^[1].
Power Play (5/89), Anatol Locker: 72% overall, but 44% for graphics and 38% for sound ^[2]^[11]. Alone it is quite fun, the review says, but the game only really comes alive with two players ^[11].

A modern retrospective on Dazeland gives it 7/10. It finds the single-player game repetitive and says the two-player modes are the reason to play ^[6].

The sequel that outshone it

Gravity Force made its biggest mark through two Swedish fans, Jens Andersson and Jan Kronquist. They played it so much, Andersson recalls, that they started making up extra rules of their own ^[4]. When they wrote a follow-up, they phoned Wenzler in Germany to ask if they could use the name. He was, they recall, "completely fine with it" ^[4].

Gravity Force 2 came out in 1994. It was a complete rewrite that shared no code with the Kingsoft original, and it added destructible walls and single-player missions, plus two-player games on a split screen or over a null-modem cable ^[1]. It was released in two versions: a freeware one and one for registered users ^[7]. Amiga Power put it on the coverdisk of issue 39 and a year later ranked it the second-best Amiga game of all time, behind Sensible Soccer ^[1]. The magazine then commissioned a slightly improved version, Gravity Power, which appeared on the coverdisk of issue 50 ^[1]^[7].

Legacy

The sequel's authors released its 680x0 source code in September 2008 and put the game and code under a CC BY-SA licence, which Wikipedia dates to 2017 ^[1]^[7]. In 2015 they made a multi-platform follow-up called Gravity Force 20, and Gravity Addict, an updated version made for Amiga Addict magazine, came out in March 2026 ^[1]. In September 2026 they added a browser version of Gravity Force 2 with online play ^[7]. Gravity Power is one of the games in the book 1001 Video Games You Must Play Before You Die (2011) ^[1].

Wenzler said in 1999 that he took the many imitations as the best compliment he could get ^[9]. Wikipedia notes freeware clones that see themselves as heirs to Gravity Force and Gravity Power rather than to Thrust ^[1]. There is also a PC remake from 2000 ^[8], and an AROS remake whose readme names Stephan Wenzler as the original author ^[5].

Sources

Drafted by Claude from the sources listed; fact-checked by Claude, not yet reviewed by a person.

Gravity Force

The story of the game

Two ships in one cave, gravity, fuel and gunships. Six ships each; the last pilot flying wins.

Play it yourself

Your name

Against

Your side (practice)

Keyboard: arrows or WASD, Space or Ctrl to fire, Shift second fire, P pause. Gamepad: stick or d-pad, A fire, B second fire, Back pause.

Ranked: a hidden start and a side drawn at random, and your rating moves (Players and Everyone boards).

Watch a match

Side A Side B

Ranked: a hidden start, sides drawn at random, ratings move. Practice: the public start, side A is Pilot 1 (top view, port 1).

Upload a bot

Bot name (or NAME in the script)

Your name

Lua source (or pick a file)

Rankings

#	Name	Author	Rating
1	reference ✓ tested	the arena	1200?	source
2	dev loic ✓ verified	dev loic	1200?
1	reference ✓ tested	the arena	1200?	source
1	dev loic ✓ verified	dev loic	1200?

One rating per game for everyone; "?" marks a rating from fewer than 10 ranked games. Human players join the rankings soon.

Recent matches

When	Side A	Side B	Result	Length
	dev loic	reference	dev loic won	1:58	practice replay

Writing a bot

A bot is Lua 5.4 text. frame(n) is called once a frame and returns the joystick lines to hold; init(port, players) runs once first; NAME = "..." names it on the picture.

NAME = "superbot"
function init(port, players) me = port end
function frame(n)
  local v = ram.u8(0x1234)        -- the game's memory, read only
  return bits.UP + bits.FIRE      -- UP 1, DOWN 2, LEFT 4, RIGHT 8, FIRE 16, FIRE2 32
end

Available: ram.u8/u16/u32(addr), ram.bytes(addr, len), bits.*, print, say(text), and Lua's base, string, table and math. No io, os, load or debug; 16 MB of memory.

Thinking out loud: say("going for the ladder") shows what the bot is thinking under the match picture, its last three thoughts per side. Only a change shows, so it is fine to call it every frame with the current plan.

Time: a frame is 20 ms and the emulator needs about 11 of them, so each frame() call has a cap of 700,000 units: a unit is one Lua instruction, and each ram.* read costs 3 more (plus one per 64 bytes). That is about 7 ms in a fast browser. A call that goes over is stopped and presses nothing that frame. A new bot is untested until a practice match of a minute or more (the "Test it now" button after an upload) shows it never goes over; only tested bots play ranked, and going over in any match untests it. The match screen shows each bot's cost as a share of the cap.

Sides: A is Pilot 1 (top view, port 1); B is Pilot 2 (bottom view, port 0). A match ends when the game's results say so, or after 5 minutes.

Start from the reference bot, the results plugin, and the public start state (load it in WinUAE or FS-UAE with the AROS ROM).