Free Tumblr Bot
I have developed an Tumblr bot on my own. It requires python (not an exe version but you can easily run it, just install python 2.7, make a google search for it)
You just have one thing: Edit the file (its like a txt) for your own options, you will see what to edit.
This tumblr bot can follow, and update queue easily for more accounts too. The bot works very fast, and have low memory /cpu compusition.
You can download it from there (its the source code): http://adf.ly/1dcLNa
If you want any help thorugh installing or how the bot works.
1. INstall python
2. Download Requests and lxml library (check google how to)
3. Run the bot