Hello, if you have a Mac, you can download UTAU-Synth from the link Zenitsu-Izuku sent to you. :)
If you want to download the original UTAU for Windows, please visit: http://utau2008.xrea.jp
v0.4.18e is the English version of UTAU.
I want to remind you that before you download and install it, you have to set your computer's locale to Japan and add the Japanese language and other configurations, otherwise UTAU won't work. There are several tutorials on UtaForum and YouTube that can help you.
Most UTAU voicebanks can be downloaded on their personal websites. Look on UTAU Wiki or UtaForum for more information.
Piapro Studio is a free VSTi (and Standalone software since Hatsune Miku V4 Chinese) included in all voicebank packages by Crypton Future Media since KAITO V3. There is Piapro Studio (for V3) and Piapro Studio for V4X. You can select and order them on Crypton's website:
https://ec.crypton.co.jp/pages/prod/vocaloid
If you mean Piapro Studio for NT, it is not released yet and is expected to be released in summer 2020.
As you probably know, you can download the Vocaloid5 Editor on https://www.vocaloid.com/en/compare/#lineup
and Voicebanks on
https://www.vocaloid.com/en/products
And I want to remind you that Vocaloid2 voicebanks are not compatible with Vocaloid5.
Well, actually there are some people who make them work on it with editing the files. But I would say it wasn't intended to. haha
I hope I could help you! ^-^