Rescan SD Card! is what I use on my devices, and I'm pretty satisfied with it. Just re-checked the details on the app's page, and see it was even updated to work with Kitkat (Android 4.4; there have been changes applied to that Android version which rendered most Rescan apps inoperable).
How does this app match your requirements?
free: It comes at no cost. ...
I'm not sure if it's any good, but I was reading about this one earlier. Seems to be brand new. Looks promising in the screenshot the author provided.
True Capacity is an open-source tool that checks flash drives and memory cards for a fake capacity. It's a Bash script, so it's not cross-platform; Linux only.
It performs 2 tests. Test 1 writes data and ...
Found so far H2testw. In general, it's in German, but English execution is possible. Mainly it's for Windows, but there are the following alternatives:
F3 (Fight Flash Fraud) by Michel Machado - an alternative to h2testw (GitHub sources),
Open source Linux software to test flash memory capacity.
F3X GUI for F3
sdspeed - SD Card Speed Test (GitHub ...
You can use Widgetsoid which can create a Unmount SD Card widget in your homescreen
You can use QuickShortCut Maker or Activity Launcher to create a short cut in your homescreen for the Unmount SD Card Activity.
Unmount SD Card activity is com.android.settings/com.android.settings.Settings$StorageSettingsActivity
You could give a try GNOME Partition Editer (GParted).
GParted Live is a small bootable GNU/Linux distribution for x86 based computers.
GParted enables you to easily manage your disk partitions:
Create partition tables, (e.g., msdos or gpt)
Create, move, copy, resize, check, label, set new UUID, and delete partitions
Enable and disable partition ...