RTP means "RunTime Package" and was intended to have an common asset library (graphics, music, sounds) shared between games to save some disk space in early distribution days (floppy disks, dial-up modems).
RTP installers are distributed by the RPG Maker vendors in their homepages and can be downloaded for free (but can't be redistributed in other places).
The better games usually don't need any files from the RTP to make them independent of requiring additional installations.
Because EasyRPG is free (as in freedom) wants to create it's own RTP replacement to be freely modified and distributed. However, EasyRPG does not have a complete RTP yet. Meanwhile you can use official RPG Maker 2000 and 2003 RTPs, but remember they are non-free and can't be redistributed or used for other projects different than RPG Maker.
This website is written in Japanese only. Scroll down to the bottom of these files and click over the long blue button to download the RTP files for each as follows:
Depending on the operating system you have to take care on a few steps:
Just install the RTP using the official installer, the Player will automatically find it (by reading the Windows registry).
IMPORTANT: Official installers are Japanese only and they are not Unicode. This means you will need to run them in a Windows Japanese environment or the installation won't work properly.
You can do this with ease with LocaleEmulator: http://i.watashi.me/archives/locale-emulator.html with Windows 7 or later. For older Windows (XP/2003) you can use AppLocale: http://www.microsoft.com/en-us/download/details.aspx?id=13209 and still install AppLocale on Windows 7 by running the msi installer with legacy operating system emulation or by following this guide
EasyRPG Player can read RTP paths from the WINE registry like RPG_RT does from the Windows registry.
To make Player read 2000 and 2003 RTPs, just install them with WINE. Once RTPs are installed you can uninstall WINE, it is only needed for a legal installation.
Because RTP are Japanese shift JIS encoded and they are not Unicode, you will need to execute them with a different locale if your UNIX default locale is not Japanese. You need to have the ja_JP.UTF-8 locale generated. Check your distribution locale configuration if you need to enable it (can vary between distributions). Once RTPs are installed you can disable this locale again.
By following the instructions below you will be able to install them:
From a terminal window, go to the working folder where RPG2000RTP.exe and RPG2003RTP.exe files have been unpacked, then run:
LANG=ja_JP.UTF-8 wine RPG2000RTP.exe
LANG=ja_JP.UTF-8 wine RPG2003RTP.exe
For systems which don't have, don't support or simply don't want to use WINE and its registry to auto detect RTP path:
You will need to copy RTP files by hand using your own method, e.g. from a preinstalled RTP.
The RTP is found by EasyRPG Player by reading these environment variables:
RPG2K_RTP_PATH: For the RPG2000 RTP
RPG2K3_RTP_PATH: For the RPG2003 RTP
RPG_RTP_PATH: For any RTP (fallback if 2k or 2k3 variable is missing)
If your system does not support environment variables you can place the RTP in the folders
Extract the RTP into
/data/rtp/2003 (SD and USB are supported).