passkb is a "virtual keyboard", which will type any string after a small delay. Its primary use-case is to paste passwords into fields, which otherwise disable paste functionality.
Disabling paste functionality for password fields is a questionable security practice, because it makes it harder to use password managers for these fields and encourages users to come up with insecure passwords. Since such password fields still need to allow users to type the password in, passkb emulates a virtual keyboard and "types" the provided password for you. So instead of pasting your secure password directly, you paste it into passkb and passkb "types" it in instead.
passkb can be downloaded and compiled using standard go get approach. Assuming you have Go installed, just
go get github.com/pqsec/passkb/cmd/passkb
The passkb binary should appear in your $GOPATH/bin directory.
Works on Linux, Windows and MacOS (on MacOS Command Line Tools for Xcode are needed to compile the binary).
You can also get a precompiled binary for your operating system from the Releases section.