In the tech world, the word "homebrew" generally refers to code written by programmers that can run on devices such as gaming consoles, or other gadgets that are not made to run unauthorized code. The running of homebrew applications on devices not intended to run unsigned code is frowned upon by much of the gaming and computers industry. For example, Sony disapproves of users running their own homebrew on the PlayStation consoles.
Homebrew games would be those written by programmers with no financial aims. Most manufacturers of games disapprove of their games being played on devices that they weren't created for, but the ability to run homebrew code on a device usually leads to such a possibility through emulators.
Hardware solutions to run homebrew
Because the games industry is plagued by piracy, anti-piracy measures usually make running homebrew code impossible, or at least at first glance. In the past decade gaming consoles such as the PS2 and XBOX have used measures to prevent unauthorized software from being run, but both systems have been beaten by the use of Modchips that can bypass the security measures.
The legality of Modchips varies around the world. Sony disapproves of consumers modifying their consoles because it makes piracy of games possible. With the security measures beaten, launching a copy of a game with most modchips is easy. Also, with Modchips providing the ability to run homebrew code, programmers have written emulators for consoles that allow games from other platforms to be played. However, modchips will also usually allow you to play imported games, which is something else that wasn't possible with an unmodified console. A recent High Court ruling in Australia decided that the extra legal things you can do with a modified console, outweigh the illegal things.
See: https://www.afterdawn.com/news/archive/6906.cfm (Modchips legal says Australian High Court)
Software solutions to run homebrew
Another example of how hackers have run homebrew on locked systems concerns Sony's latest console offering, the PlayStation Portable (PSP). The original PSP firmware allowed the running of homebrew without the need for exploits. However, an updated firmware, v1.50 changed that, locking out homebrew code. That didn't stop the hackers however, who through the use of exploits could launch homebrew on PSP 1.50.
See: https://www.afterdawn.com/news/archive/6556.cfm (PSP v1.50 firmware cracked).
Two later versions of the firmware, v1.51 and v1.52 fixed the problem for Sony, and were a nuisance to users who bought their brand new PSPs to discover they had been sold with either of these firmware versions. Some months later, Sony released the next version of the firmware, v2.00.
See: https://www.afterdawn.com/news/archive/6763.cfm (Sony releases PSP 2.0 update in North America)
Once again, hackers got the better of Sony. A flaw discovered in the image viewer allowed some homebrew code to be run. The first homebrew code to run on PSP 2.00 only changed the colour of the PSP screen. However, that was enough to excite 2.00 users as it was simple proof of concept.
See: https://www.afterdawn.com/news/archive/6855.cfm (Progress being made with PSP v2.0 cracking)
Finally a solution emerged for 2.0 users. A downgrader (by MPH) was released which made it possible to change the PSPs firmware to v1.50. Though the process did show some error messages and came with a warning, it still has not shown any major problems for PSP users who downgraded, and can also be safely upgraded again. Also, homebrew code runs perfectly on a downgraded PSP.
See: https://www.afterdawn.com/news/archive/6861.cfm (Downgrade PSP 2.0 to PSP 1.50)
Sony will continue to fight against homebrew being launched on a PSP. It is not surprising that so far, PSPs have not required a hardware solution (like modchips) to bypass security measures. Compare the PSP against the PS2 and XBOX, what are the major differences? The PS2 and XBOX were merely gaming consoles (expect for offering some music features and others) whereas Sony has created the PSP as a portable entertainment device that can do more than play games. With a PSP you can listen to music, view photos, watch videos, browse the internet (with firmware above 2.00) through a wireless network and the latest PSP firmware (2.50) has come even more feature packed.
See: https://www.afterdawn.com/news/archive/6943.cfm (Sony releases PSP 2.50 firmware)
Also you can store any files on a Memory Stick, provided that you have enough free space. Therefore all these extra features meant that some bugs that could be exploited, most likely exist. When they are found by hackers, another solution is created to run homebrew code on a proprietary platform.
Another example of how a software flaw led to the possibility of running homebrew, is the PS2 Independence Exploit. Some versions of the PS2 console had a buffer overflow bug in the BIOS. Hackers discovered how to modify a file (TITLE.DB) to trigger a buffer overflow and ultimately run code from a Memory Card (unencrypted) when a specific PS1 game was run.
This allowed homebrew to be run on an unmodified console. Sony corrected the problem, but using a Modchips with a PS2 is by far the best way to launch homebrew code on the console.
Manufacturers will probably never stop their customers from finding ways of running unauthorized code on their products; homebrew is most likely here to stay.
As more major developments happen with homebrew code, this glossary item will be updated.