The Lubuntu web site (https://lubuntu.me/downloads/) has available
- Desktop 64-bit (amd64)
- Desktop 32-bit (x86 also called i386)
- Desktop Alternate (x86 & amd64)
- Raspberry Pi (model 2 & 3)
Available firstly is the current Lubuntu 18.04 LTS using LXDE desktop, or legacy Lubuntu. The standard (32-bit & 64-bit) desktop use the standard Ubuntu
ubiquity installer, the alternate installer uses debian-installer.
The ubiquity installer runs on a 'live' system, which requires ~700MB just for the live PLUS the memory required for the installer (so total is ~1gb)
The alternate installer has NO live system, thus is useful for machines with <700MB of ram. Note: The alternate installer was last created for 18.04 (not later 18.04.1-18.04.3) so will require loads of updates post or during install. Live installers are available with 18.04.3 (currently the latest).
The original 18.04 & 18.04.1 do not include HWE kernel (hardware enablement stack - see https://wiki.ubuntu.com/Kernel/LTSEnablementStack), the 18.04.2 & 18.04.3 have HWE enabled turned on, meaning later kernel & software stacks useful for more modern hardware.
Modern Lubuntu 19.10 uses the LXQt desktop and is only available in amd64 (or x86_64). It's called amd64 because AMD created the 64-bit architecture used by both AMD and INTEL (Intel's competing IA64 failed in the marketplace due to lack of backward compatibility)
Also available is the Raspberry Pi 2 & 3.
I don't see PowerPC - were you looking at the Official Lubuntu web site? If you're unsure, don't use google (it could send you to a 'fan' site), but use ubuntu.com where https://ubuntu.com/download/flavours will go to official sites for different flavors.
The x86 (32-bit), amd64 (x86_64), armv(7 & 8), arm64, s390, powerpc, ppc64el are different architectures. Most PCs are amd64 today; powerpc is EOL being replaced by ppc64el (ppc 64-bit) which is incompatible
Lubuntu 18.04 LTS choice (Notes)
- It's a LTS or long-term-support release, supported until 2021-April (3 years from release in 2018-April)
- LXDE is light & fast, but uses old GTK+2 which most modern applications haven't used in years, so some of lightness maybe lost when apps are added
- traditional desktop known & loved by many users
- LXDE is mostly abandoned, or on life-support, few updates
- will likely require re-install to move to modern Lubuntu with LXQt (currently unsupported upgrade, this may change but I suspect not)
- x86 and amd64 support (ie. 32-bit)
Lubuntu 19.10 choice (Notes)
- a short term release, supported until 2020-July only
- has upgrade path to Lubuntu 20.04 LTS
- now amd64 only (no 32-bit x86/i386)
- is very light; I tested 18.10 & 19.04 on x86 laptops with only 1GB of RAM & was happy
- has manual available http://manual.lubuntu.me/
- more modern LXQt desktop
- Some members of the Lubuntu team are more interested in LXQt & supporting it (rather subjective opinion)
- uses modern Qt5 framework, so does mean KDE or Qt apps will be lighter; alas modern GTK+3 apps won't be as light, but they weren't always real light on LXDE with it's GTK+2 desktop anyway
- better modern GTK3 & Qt theme support