Hi,
Thinking about using nextcloud via goodcloud rovider for my personal email etc… What I don’t understand is if nextcloud uses libreoffice as its “offline apps” or if it has its own builds/versions? And are there mobile apps for same purpose?
If you mean desktop applications, then it doesn’t really matter which office suite you use. You would simply install the Nextcloud desktop sync client, which synchronizes your files with your Nextcloud instance and from there with other devices that also have the client installed. So you can use any desktop office application you like.
However, Nextcloud has the option to add an online (browser-based) office suite to the server: either Nextcloud Office (Collabora Online, which is based on LibreOffice) or ONLYOFFICE. For that, you would need to check with The Good Cloud whether this is included in the specific plan you’re considering.
If Nextcloud Office (or ONLYOFFICE) is installed on the server, you can open and edit office documents that are stored on the server directly in the Nextcloud mobile app. If not, it works the same way as on the desktop: you simply use any office app you prefer, and Nextcloud would then only be responsible for file synchronization.
As for the email part, Nextcloud itself does not provide an email server. It only offers a web-based email client that connects to existing email accounts via IMAP, so the messages themselves remain on the servers of the respective email providers.
Nextcloud also does not provide dedicated desktop or mobile email clients. On your client devices, you can either use the Nextcloud web UI or any other desktop or mobile email client you prefer.
EDIT:
By the way, just like with Nextcloud Office, you should also check with your provider whether Nextcloud Mail is included in your plan or can be installed. Not all providers offer all apps, or allow app installation on every plan. Lower tier plans and free accounts in particular are usually very limited and often restricted to basic file synchronization, and possibly calendar and contact synchronization.
If the hoster also allows WebDAV-access, you may use f.ex. LibreOffice as “offline” client. LibreOffice can be configured to access Nextcloud via WebDAV as “normal” storage.
If you choose Collabora or Onlyoffice online, you can hande your documents online but you also may switch to LibreOffice as offline client while your device is connected online.