We will use Keyman as the input tool. Keyman input tool is an opensource input mechanism developed by SIL.
# All in one installer
Download Keyman Desktop and Swanalekha Malayalam in a single installer:
# Installing swanalekha and keyman seperately
Download the Swanalekha keyman input method. Use the download button below.Download Swanalekha Keyman
Start the Keyman. Open Keyman Configuration, from the Keyman menu (on the Windows Taskbar near the clock).
Select the Keyboard Layouts tab. Click Install Keyboard and choose the swanalekha keyboard downloaded. You may also follow detailed documentation from their website.
Now open any application where you want to type Malayalam. From the keyman icon, Choose "Swanalekha Malayalam". Now you can type in Manglish anywhere and you will see malayalam.
# Video tutorial
Here is a video illustrating installation and usage.