maildir helps me to open instances (tty ~ i believe) without messing my emails.

where and how can i find other packages which have similar functionality.

regards

Please clarify. Instances of what? What does it mean "without messing emails"? To me, Maildir folders is an email storage format. There are many tools (both CLI and GUI) that can work with it, but I don't know of a command named maildir.

Moreover, package searching tools will often depend on your distribution. What distro are you using? What are your requirements? Should the search be restricted to official distribution repositories only? Also include third party repos? Are you OK using AppImages/Snaps/Flatpaks? Building software from source?

yes, we have to specify "maildir" format in mutt and in thundebird (its experimental with many issues on bugzilla).

use case: in order to make habit of cli, i want to use two or more virtual terminals. in one terminal, i will compile my package. in second terminal (t2), i will read about specific issues or guides using web browser (lynx) and check mails. if i shift to terminal 1 (t1), if compile is sucessful, i might check mail or use browser to read how to compile other package. so if i use mutt with maildir, i am worry free. my query: can i use lynx in both t1 and t2.

what packages can be used or what key word should i use to search for packages that support running or to use simultaneously in two terminals.

Now, I'm confused. What has all this to do with Maildir? Sure, you can run Lynx in both terminals, and you don't need any additional software for this.

Some terminal emulators allow running multiple terminal windows within the same process to conserve resources (urxvtd, mlclient, LXTerminal, LilyTerm). Others allow dividing one window into multiple panes (Terminator, Tilix, QTerminal, kitty, Terminology, Deepin Terminal, Konsole).

OTOH, there are terminal multiplexers and text-mode window managers (Screen, tmux, Byobu, dvtm), or more basic tools like splitvt. They don't require GUI and could be run on the console.

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As has been said, Maildir is a format for storing email on a server. It is used by qmail and dovecot...I’m sure there are others.
I’ve never had to tell an email client (mutt, Thunderbird, Outlook, etc.) that the server is using Maildir, so I’m also confused about what the OP needs help with.

After sleeping on it, I guess I can somehow deduce OP's intent.

@OP. If you just gave Maildir as an example of a format that allows different processes simultaneously access the same data without interfering with each other, then I have a good news for you: Linux is not Windows. It's somewhat common for a Windows application to exclusively lock a file on open, effectively preventing anything else from accessing it. But in Linux (or speaking more broadly, in Unix-like OSes generally) such behavior is rare. Heck, you often can delete a file, while it's still being opened by another process, and the system will handle this situation gracefully. Two recent threads here on LQ discuss a bug in the nvi text editor that prevents you from running a script while editing it in another terminal window. And everybody agrees this is a bug that needs fixing.

Of course, Linux also has mechanisms to compartmentalize resources and to isolate processes from each other (cgroups, containers, chroot jails, whatever), but I doubt the setup you described requires any of them.

And as scasey pointed out above, you probably have a misconception about what Maildir is used for, thus making it difficult to understand you. You see, the usual email setup nowadays is that all your mails are kept on a remote IMAP server, and your email client just fetches them from there as needed. The email storage format on the server is not of your concern as the end user. Some email clients may let you choose the format for locally stored emails. They do this in order to ease import/export/interoperability between different mail processing tools. I wonder what are you going to do with those locally stored emails that you want to keep them in Maildir format so badly? Some sort of automatic post-processing done as a background job?

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@shruggy you are on spot. i want it badly so i can i read or delete or reply from any terminal. i assumed most packages does not support. in your own words: i am looking for packages or format that allows different processes simultaneously access the same data without interfering with each other

its good to know i can choose a specific clone and learn from scratch how to utilise it.

Mail has the advantage that it is read, written or deleted - but never modified in place.
So it is relatively easy to arrange for multiple users to access it, without any great problems occurring.

Simultaneous access is not a function of the format, as far as I know, but a function of the application/process. IMAP should work with the mbox format, for example.
“ allows different processes simultaneously access the same data without interfering with each other” is too general a requirement, IMO. A specific example of the problem you’re trying to solve might elicit more helpful responses, I’m thinkin’.

i willl come back with specific issue (with error). thanks for all updating my knowledge.