This plugin is just what it says. It takes MIDI event input and writes
MIDI event output in the form of an arpeggio over the held keys in the
input. You can control the speed of the arpeggio and the direction (up
or down).

A plugin that converts a LV2 control port value to MIDI CC events. You
can set the CC number and the expected range of the input value.

A MIDI keyboard. You can use it to send pitchbend events, CC events and
of course notes, using mouse or keyboard. Handy when you want to test a
synth patch but don't have a real keyboard nearby. Klaviatur has a Gtk
GUI that you use to control it.

A set of plugins that output constant control parameters for
mathematical constants defined in the C header .

A set of plugins wrapping most of the functions in the C header 
(sin(), cos(), exp(), modf() etc). All are available as both audio rate
and control rate functions.

A decaying peak meter that shows the peak level of the input signal.
There is a mono and a stereo version. Both have Gtk GUIs.

A simple drum machine with six separate drum voices - two bass drums,
two snares and two hihats. The different voices are mapped to C, D, E,
F, G and A in all octaves, and every voice has three control parameters
(length, hardness and volume). This plugin has a Gtk GUI that you can
use to control the parameters.

An LV2 version of the Sineshaper synth - two sine oscillators fed
through two sine waveshapers in series, with a bunch of parameters to
control them. This plugin has a Gtk GUI too.

The host that comes with this package is called Elven (Experimental LV2
Execution ENvironment). It is pretty slow and I don't really recommend
it. If you can use another host, do that.