Imagine if for a realtime strategy game, for reaserch and some fun a tool has been made which monitors the minimap of the game and warns the user if the enemy movement is being detected.
Does selling and/or distributing such stuff have legal issues, against the game creators ToS or such (Considering its usage in multiplayer)?
This is quite dependent on the game's terms of use (they might forbid those tools).
A random sampling says:
Blizzard says:
You agree that you will not, under any circumstances: [...] use cheats, automation software (bots), hacks, mods or any other unauthorized third-party software designed to modify the World of Warcraft experience;
EA says:
You may violate the Terms of Service if, as determined by EA in its sole discretion, you: [...]
- Promote, encourage or take part in any activity involving hacking, cracking, phishing, taking advantage of exploits or cheats and/or distribution of counterfeit software and/or virtual currency/items.
Zynga says:
CHEATING AND HACKING - You agree that you will not, under any circumstances:
[...]
d. Use cheats, exploits, automation software, bots, hacks, mods or any unauthorized third party software designed to modify or interfere with the Service or any Zynga game experience;
Even if the game's terms of use don't allow those tools, there's the subjective aspect: some gamers will consider those tools unethical and look down on anybody who uses them.
As stated on a comment, while in singleplayer games they'd be OK, in multiplayer games they will most likely seen as cheating.
To add to Renan's response, deliberately violating the ToS (assuming you agree to it) is fraud.
